Use concurrently to run start script with GCP telemetry (#1329)

## TLDR

Introduces the `concurrently` package to simplify the dev startup process with GCP telemetry enabled.

## Dive Deeper

Previously, developers had to run the telemetry script and the main application start script in separate terminals. This change updates the `start:gcp` script to use `concurrently`, allowing both processes to be launched and managed with a single command. This improves the developer experience and reduces the chance of forgetting to start one of the required processes. 

## Reviewer Test Plan
Set the required environment variable:

```shell
export OTLP_GOOGLE_CLOUD_PROJECT=<your-project-id>
```

Run the following command:

```shell
npm run start:gcp
```

#750 

cc @teeler 

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