Add telemetry command and refactor telemetry settings (#1060)

#750 

### Telemetry Settings
Refactors telemetry configuration to use a nested `telemetry` object in `settings.json`, for example:

```json
{
  "telemetry": {
    "enabled": true,
    "target": "gcp"
    "log-prompts": "true"
  },
  "sandbox": false
}
```

The above includes
- Centralized telemetry settings under a `telemetry` object in `settings.json`.
- CLI flags for the `gemini` command to override all telemetry sub-settings:
    - `--telemetry` / `--no-telemetry`
    - `--telemetry-target <local|gcp>`
    - `--telemetry-otlp-endpoint <URL>`
    - `--telemetry-log-prompts` / `--no-telemetry-log-prompts`
- Updates `packages/cli/src/config/config.ts` and `packages/core/src/config/config.ts` to read from the new settings structure and respect the new CLI flags.
- Modifies `scripts/handle-telemetry.js`, `scripts/local_telemetry.js`, and `scripts/telemetry_utils.js` to align with the new settings structure.
- Updates `docs/core/telemetry.md` to reflect the new settings structure, CLI flags, and order of precedence.
- Renames `logUserPromptsEnabled` to `logPrompts` for brevity.

### `npm run telemetry`

Add a new `npm run telemetry` command that uses `scripts/telemetry.js`, automates the entire process of setting up a local and GCP telemetry pipelines, including configuring the necessary settings in the `.gemini/settings.json` workspace file and installing required binaries (e.g. `otelcol-contrib`).

---
```shell
$ npm run telemetry -- --target=gcp

> [email protected] telemetry
> node scripts/telemetry.js --target=gcp

⚙️  Using command-line target: gcp
🚀 Running telemetry script for target: gcp.
✨ Starting Local Telemetry Exporter for Google Cloud ✨
⚙️  Enabled telemetry in workspace settings.
🔧 Set telemetry OTLP endpoint to http://localhost:4317.
🎯 Set telemetry target to gcp.
✅ Workspace settings updated.
✅ Using Google Cloud Project ID: foo-bar

🔑 Please ensure you are authenticated with Google Cloud:
  - Run `gcloud auth application-default login` OR ensure `GOOGLE_APPLICATION_CREDENTIALS` environment variable points to a valid service account key.
  - The account needs "Cloud Trace Agent", "Monitoring Metric Writer", and "Logs Writer" roles.
✅ otelcol-contrib already exists at /Users/jerop/github/gemini-cli/.gemini/otel/bin/otelcol-contrib
🧹 Cleaning up old processes and logs...
✅ Deleted old GCP collector log.
📄 Wrote OTEL collector config to /Users/jerop/github/gemini-cli/.gemini/otel/collector-gcp.yaml
🚀 Starting OTEL collector for GCP... Logs: /Users/jerop/github/gemini-cli/.gemini/otel/collector-gcp.log
⏳ Waiting for OTEL collector to start (PID: 17013)...
✅ OTEL collector started successfully on port 4317.

✨ Local OTEL collector for GCP is running.

🚀 To send telemetry, run the Gemini CLI in a separate terminal window.

📄 Collector logs are being written to: /Users/jerop/github/gemini-cli/.gemini/otel/collector-gcp.log

📊 View your telemetry data in Google Cloud Console:
   - Logs: https://console.cloud.google.com/logs/query;query=logName%3D%22projects%2Ffoo-bar%2Flogs%2Fgemini_cli%22?project=foo-bar
   - Metrics: https://console.cloud.google.com/monitoring/metrics-explorer?project=foo-bar
   - Traces: https://console.cloud.google.com/traces/list?project=foo-bar

Press Ctrl+C to exit.
^C
👋 Shutting down...
⚙️  Disabled telemetry in workspace settings.
🔧 Cleared telemetry OTLP endpoint.
🎯 Cleared telemetry target.
✅ Workspace settings updated.
🛑 Stopping otelcol-contrib (PID: 17013)...
✅ otelcol-contrib stopped.
```

1 files changed, 42 insertions, 23 deletions

diff --git a/docs/core/telemetry.md b/docs/core/telemetry.md
index c2c69eb9..c42c2ed6 100644
--- a/docs/core/telemetry.md
+++ b/docs/core/telemetry.md
@@ -15,19 +15,19 @@ This entire system is built on the **[OpenTelemetry] (OTEL)** standard, allowing
     - You have exported the `GOOGLE_CLOUD_PROJECT` environment variable.
     - You have authenticated with Google Cloud and have the necessary IAM roles.
       For full details, see the [Google Cloud](#google-cloud) prerequisites.
-2.  **Run the Script:** Execute the following command from the project root:
+1.  **Run the Command:** Execute the following command from the project root:
     ```bash
-    ./scripts/telemetry_gcp.js
+    npm run telemetry -- --target=gcp
     ```
-3.  **Run Gemini CLI:** In a separate terminal, run your Gemini CLI commands. This will generate telemetry data that the collector will capture.
-4.  **View Data:** The script will provide links to view your telemetry data (traces, metrics, logs) in the Google Cloud Console.
-5.  **Details:** Refer to documentation for telemetry in [Google Cloud](#google-cloud).
+1.  **Run Gemini CLI:** In a separate terminal, run your Gemini CLI commands. This will generate telemetry data that the collector will capture.
+1.  **View Data:** The script will provide links to view your telemetry data (traces, metrics, logs) in the Google Cloud Console.
+1.  **Details:** Refer to documentation for telemetry in [Google Cloud](#google-cloud).
 
 ### Local Telemetry with Jaeger UI (for Traces)
 
-1.  **Run the Script:** Execute the following command from the project root:
+1.  **Run the Command:** Execute the following command from the project root:
     ```bash
-    ./scripts/local_telemetry.js
+    npm run telemetry -- --target=local
     ```
 2.  **Run Gemini CLI:** In a separate terminal, run your Gemini CLI commands. This will generate telemetry data that the collector will capture.
 3.  **View Logs/Metrics:** Check the `.gemini/otel/collector.log` file for raw logs and metrics.
@@ -42,16 +42,35 @@ You can enable telemetry in multiple ways. [Configuration](configuration.md) is
 
 **Order of Precedence:**
 
-1.  **CLI Flag (`--telemetry`):** These override all other settings for the current session.
-2.  **Workspace Settings File (`.gemini/settings.json`):** If no CLI flag is used, the `telemetry` value from this project-specific file is used.
-3.  **User Settings File (`~/.gemini/settings.json`):** If not set by a flag or workspace settings, the value from this global user file is used.
-4.  **Default:** If telemetry is not configured by a flag or in any settings file, it is disabled.
+Telemetry settings are resolved in the following order (highest precedence first):
 
-Add these lines to enable telemetry by in workspace (`.gemini/settings.json`) or user (`~/.gemini/settings.json`) settings:
+1.  **CLI Flags (for `gemini` command):**
+    - `--telemetry` / `--no-telemetry`: Overrides `telemetry.enabled`. If this flag is not provided, telemetry is disabled unless enabled in settings files.
+    - `--telemetry-target <local|gcp>`: Overrides `telemetry.target`.
+    - `--telemetry-otlp-endpoint <URL>`: Overrides `telemetry.otlpEndpoint`.
+    - `--telemetry-log-prompts` / `--no-telemetry-log-prompts`: Overrides `telemetry.logPrompts`.
+2.  **Environment Variables:**
+    - `OTEL_EXPORTER_OTLP_ENDPOINT`: Overrides `telemetry.otlpEndpoint` if no `--telemetry-otlp-endpoint` flag is present.
+3.  **Workspace Settings File (`.gemini/settings.json`):** Values from the `telemetry` object in this project-specific file.
+4.  **User Settings File (`~/.gemini/settings.json`):** Values from the `telemetry` object in this global user file.
+5.  **Defaults:** applied if not set by any of the above.
+    - `telemetry.enabled`: `false`
+    - `telemetry.target`: `local`
+    - `telemetry.otlpEndpoint`: `http://localhost:4317`
+    - `telemetry.logPrompts`: `true`
+
+**For the `npm run telemetry -- --target=<gcp|local>` script:**
+The `--target` argument to this script _only_ overrides the `telemetry.target` for the duration and purpose of that script (i.e., choosing which collector to start). It does not permanently change your `settings.json`. The script will first look at `settings.json` for a `telemetry.target` to use as its default.
+
+**Example settings:**
+Add these lines to configure telemetry in your workspace (`.gemini/settings.json`) or user (`~/.gemini/settings.json`) settings for GCP:
 
 ```json
 {
-  "telemetry": true,
+  "telemetry": {
+    "enabled": true,
+    "target": "gcp"
+  },
   "sandbox": false
 }
 ```
@@ -80,13 +99,13 @@ mkdir .gemini/otel
 
 ### Local
 
-Use the `scripts/local_telemetry.js` script that automates the entire process of setting up a local telemetry pipeline, including configuring the necessary settings in your `.gemini/settings.json` file. The script installs `otelcol-contrib` (The OpenTelemetry Collector) and `jaeger` (The Jaeger UI for viewing traces). To use it:
+Use the `npm run telemetry -- --target=local` command which automates the entire process of setting up a local telemetry pipeline, including configuring the necessary settings in your `.gemini/settings.json` file. The underlying script installs `otelcol-contrib` (The OpenTelemetry Collector) and `jaeger` (The Jaeger UI for viewing traces). To use it:
 
-1.  **Run the Script**:
-    Execute the script from the root of the repository:
+1.  **Run the Command**:
+    Execute the command from the root of the repository:
 
     ```bash
-    ./scripts/local_telemetry.js
+    npm run telemetry -- --target=local
     ```
 
     The script will:
@@ -110,7 +129,7 @@ Use the `scripts/local_telemetry.js` script that automates the entire process of
 
 ### Google Cloud
 
-For a streamlined setup targeting Google Cloud, use the `scripts/telemetry_gcp.js` script which automates setting up a local OpenTelemetry collector that forwards data to your Google Cloud project.
+Use the `npm run telemetry -- --target=gcp` command which automates setting up a local OpenTelemetry collector that forwards data to your Google Cloud project, including configuring the necessary settings in your `.gemini/settings.json` file. The underlying script installs `otelcol-contrib`. To use it:
 
 1.  **Prerequisites**:
 
@@ -122,11 +141,11 @@ For a streamlined setup targeting Google Cloud, use the `scripts/telemetry_gcp.j
     - Authenticate with Google Cloud (e.g., run `gcloud auth application-default login` or ensure `GOOGLE_APPLICATION_CREDENTIALS` is set).
     - Ensure your account/service account has the necessary roles: "Cloud Trace Agent", "Monitoring Metric Writer", and "Logs Writer".
 
-2.  **Run the Script**:
-    Execute the script from the root of the repository:
+2.  **Run the Command**:
+    Execute the command from the root of the repository:
 
     ```bash
-    ./scripts/telemetry_gcp.js
+    npm run telemetry -- --target=gcp
     ```
 
     The script will:
@@ -172,7 +191,7 @@ These are timestamped records of specific events.
     - `api_key_enabled` (boolean)
     - `vertex_ai_enabled` (boolean)
     - `code_assist_enabled` (boolean)
-    - `log_user_prompts_enabled` (boolean)
+    - `log_prompts_enabled` (boolean)
     - `file_filtering_respect_git_ignore` (boolean)
     - `debug_mode` (boolean)
     - `mcp_servers` (string)
@@ -181,7 +200,7 @@ These are timestamped records of specific events.
 
   - **Attributes**:
     - `prompt_length`
-    - `prompt` (except if `log_user_prompts_enabled` is false)
+    - `prompt` (except if `log_prompts_enabled` is false)
 
 - `gemini_cli.tool_call`: Fired for every function call.