Refactor: Use telemetry_utils.js in local_telemetry.js (#1066)

## TLDR

Refactors `scripts/local_telemetry.js` to use shared helper functions and constants from `scripts/telemetry_utils.js`.

## Dive Deeper

This change centralizes common telemetry-related logic, including:
- Binary downloading and management (`ensureBinary`)
- Reading and writing JSON files
- Waiting for network ports
- Managing workspace telemetry settings (`manageTelemetrySettings`)
- Process cleanup and signal handling (`registerCleanup`)

By using the shared utilities, `local_telemetry.js` becomes more concise and focused on its specific task of setting up the local OpenTelemetry and Jaeger environment.

## Docs

https://github.com/google-gemini/gemini-cli/blob/main/docs/core/telemetry.md#local-telemetry-with-jaeger-ui-for-traces

## Issue

#750