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

> gemini-cli@0.1.0 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.
```

packages/core/src/config/config.ts

@@ -23,7 +23,12 @@ import { GeminiClient } from '../core/client.js';
 import { GEMINI_CONFIG_DIR as GEMINI_DIR } from '../tools/memoryTool.js';
 import { FileDiscoveryService } from '../services/fileDiscoveryService.js';
 import { GitService } from '../services/gitService.js';
-import { initializeTelemetry } from '../telemetry/index.js';
+import {
+  initializeTelemetry,
+  DEFAULT_TELEMETRY_TARGET,
+  DEFAULT_OTLP_ENDPOINT,
+  TelemetryTarget,
+} from '../telemetry/index.js';
 import { DEFAULT_GEMINI_EMBEDDING_MODEL } from './models.js';
 
 export enum ApprovalMode {
@@ -40,6 +45,13 @@ export interface BugCommandSettings {
   urlTemplate: string;
 }
 
+export interface TelemetrySettings {
+  enabled?: boolean;
+  target?: TelemetryTarget;
+  otlpEndpoint?: string;
+  logPrompts?: boolean;
+}
+
 export class MCPServerConfig {
   constructor(
     // For stdio transport
@@ -82,9 +94,7 @@ export interface ConfigParameters {
   showMemoryUsage?: boolean;
   contextFileName?: string | string[];
   accessibility?: AccessibilitySettings;
-  telemetry?: boolean;
-  telemetryLogUserPromptsEnabled?: boolean;
-  telemetryOtlpEndpoint?: string;
+  telemetry?: TelemetrySettings;
   fileFilteringRespectGitIgnore?: boolean;
   checkpoint?: boolean;
   proxy?: string;
@@ -114,9 +124,7 @@ export class Config {
   private approvalMode: ApprovalMode;
   private readonly showMemoryUsage: boolean;
   private readonly accessibility: AccessibilitySettings;
-  private readonly telemetry: boolean;
-  private readonly telemetryLogUserPromptsEnabled: boolean;
-  private readonly telemetryOtlpEndpoint: string;
+  private readonly telemetrySettings: TelemetrySettings;
   private readonly geminiClient: GeminiClient;
   private readonly fileFilteringRespectGitIgnore: boolean;
   private fileDiscoveryService: FileDiscoveryService | null = null;
@@ -147,11 +155,13 @@ export class Config {
     this.approvalMode = params.approvalMode ?? ApprovalMode.DEFAULT;
     this.showMemoryUsage = params.showMemoryUsage ?? false;
     this.accessibility = params.accessibility ?? {};
-    this.telemetry = params.telemetry ?? false;
-    this.telemetryLogUserPromptsEnabled =
-      params.telemetryLogUserPromptsEnabled ?? true;
-    this.telemetryOtlpEndpoint =
-      params.telemetryOtlpEndpoint ?? 'http://localhost:4317';
+    this.telemetrySettings = {
+      enabled: params.telemetry?.enabled ?? false,
+      target: params.telemetry?.target ?? DEFAULT_TELEMETRY_TARGET,
+      otlpEndpoint: params.telemetry?.otlpEndpoint ?? DEFAULT_OTLP_ENDPOINT,
+      logPrompts: params.telemetry?.logPrompts ?? true,
+    };
+
     this.fileFilteringRespectGitIgnore =
       params.fileFilteringRespectGitIgnore ?? true;
     this.checkpoint = params.checkpoint ?? false;
@@ -167,7 +177,7 @@ export class Config {
     this.toolRegistry = createToolRegistry(this);
     this.geminiClient = new GeminiClient(this);
 
-    if (this.telemetry) {
+    if (this.telemetrySettings.enabled) {
       initializeTelemetry(this);
     }
   }
@@ -272,15 +282,19 @@ export class Config {
   }
 
   getTelemetryEnabled(): boolean {
-    return this.telemetry;
+    return this.telemetrySettings.enabled ?? false;
   }
 
-  getTelemetryLogUserPromptsEnabled(): boolean {
-    return this.telemetryLogUserPromptsEnabled;
+  getTelemetryLogPromptsEnabled(): boolean {
+    return this.telemetrySettings.logPrompts ?? true;
   }
 
   getTelemetryOtlpEndpoint(): string {
-    return this.telemetryOtlpEndpoint;
+    return this.telemetrySettings.otlpEndpoint ?? DEFAULT_OTLP_ENDPOINT;
+  }
+
+  getTelemetryTarget(): TelemetryTarget {
+    return this.telemetrySettings.target ?? DEFAULT_TELEMETRY_TARGET;
   }
 
   getGeminiClient(): GeminiClient {