Add option to disable sending usage telemetry

### Describe the feature or problem you'd like to solve

As a user, I want to be able to control what information I share with third parties.

### Proposed solution

Add a boolean `enableTelemetry` flag to `settings.json` to disable sending usage telemetry. This mirrors the existing flag in the Jetbrains GitHub Copilot plugin.

While I believe all such telemetry must be explicitly opt-in by default, at least adding the option would be a great first start, even if you don't expose it in the UI.

### Example prompts or workflows

_No response_

### Additional context

_No response_