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

package-lock.json

@@ -18,6 +18,7 @@
         "@types/mime-types": "^2.1.4",
         "@types/minimatch": "^5.1.2",
         "@vitest/coverage-v8": "^3.1.1",
+        "concurrently": "^9.2.0",
         "cross-env": "^7.0.3",
         "esbuild": "^0.25.0",
         "eslint": "^9.24.0",
@@ -3817,6 +3818,48 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/concurrently": {
+      "version": "9.2.0",
+      "resolved": "https://registry.npmjs.org/concurrently/-/concurrently-9.2.0.tgz",
+      "integrity": "sha512-IsB/fiXTupmagMW4MNp2lx2cdSN2FfZq78vF90LBB+zZHArbIQZjQtzXCiXnvTxCZSvXanTqFLWBjw2UkLx1SQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "chalk": "^4.1.2",
+        "lodash": "^4.17.21",
+        "rxjs": "^7.8.1",
+        "shell-quote": "^1.8.1",
+        "supports-color": "^8.1.1",
+        "tree-kill": "^1.2.2",
+        "yargs": "^17.7.2"
+      },
+      "bin": {
+        "conc": "dist/bin/concurrently.js",
+        "concurrently": "dist/bin/concurrently.js"
+      },
+      "engines": {
+        "node": ">=18"
+      },
+      "funding": {
+        "url": "https://github.com/open-cli-tools/concurrently?sponsor=1"
+      }
+    },
+    "node_modules/concurrently/node_modules/supports-color": {
+      "version": "8.1.1",
+      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-8.1.1.tgz",
+      "integrity": "sha512-MpUEN2OodtUzxvKQl72cUF7RQ5EiHsGvSsVG0ia9c5RbWGL2CI4C7EpPS8UTBIplnlzZiNuV56w+FuNxy3ty2Q==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "has-flag": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/supports-color?sponsor=1"
+      }
+    },
     "node_modules/config-chain": {
       "version": "1.1.13",
       "resolved": "https://registry.npmjs.org/config-chain/-/config-chain-1.1.13.tgz",
@@ -8852,6 +8895,16 @@
         "queue-microtask": "^1.2.2"
       }
     },
+    "node_modules/rxjs": {
+      "version": "7.8.2",
+      "resolved": "https://registry.npmjs.org/rxjs/-/rxjs-7.8.2.tgz",
+      "integrity": "sha512-dhKf903U/PQZY6boNNtAGdWbG85WAbjT/1xYoZIC7FAY0yWapOBQVsVrDl58W86//e1VpMNBtRV4MaXfdMySFA==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "dependencies": {
+        "tslib": "^2.1.0"
+      }
+    },
     "node_modules/safe-array-concat": {
       "version": "1.1.3",
       "resolved": "https://registry.npmjs.org/safe-array-concat/-/safe-array-concat-1.1.3.tgz",
@@ -9888,6 +9941,16 @@
         "tslib": "2"
       }
     },
+    "node_modules/tree-kill": {
+      "version": "1.2.2",
+      "resolved": "https://registry.npmjs.org/tree-kill/-/tree-kill-1.2.2.tgz",
+      "integrity": "sha512-L0Orpi8qGpRG//Nd+H90vFB+3iHnue1zSSGmNOOCh1GLJ7rUKVwV2HvijphGQS2UmhUZewS9VgvxYIdgr+fG1A==",
+      "dev": true,
+      "license": "MIT",
+      "bin": {
+        "tree-kill": "cli.js"
+      }
+    },
     "node_modules/ts-api-utils": {
       "version": "2.1.0",
       "resolved": "https://registry.npmjs.org/ts-api-utils/-/ts-api-utils-2.1.0.tgz",

package.json

@@ -40,7 +40,7 @@
     "publish:npm": "npm publish --workspaces ${NPM_PUBLISH_TAG:+--tag=$NPM_PUBLISH_TAG} ${NPM_DRY_RUN:+--dry-run}",
     "publish:release": "npm run build:packages && npm run prepare:cli-packagejson && npm run build:docker && npm run publish:sandbox && npm run publish:npm",
     "telemetry": "node scripts/telemetry.js",
-    "start:gcp": "npm run telemetry -- --target=gcp & npm start"
+    "start:gcp": "concurrently --raw --kill-others \"npm run telemetry -- --target=gcp\" \"npm start\""
   },
   "bin": {
     "gemini": "bundle/gemini.js"
@@ -55,6 +55,7 @@
     "@types/mime-types": "^2.1.4",
     "@types/minimatch": "^5.1.2",
     "@vitest/coverage-v8": "^3.1.1",
+    "concurrently": "^9.2.0",
     "cross-env": "^7.0.3",
     "esbuild": "^0.25.0",
     "eslint": "^9.24.0",