## Summary of the Pull Request
- [x] Implements `GithubCopilotLLMProvider`, which is an implementation
of `ILMProvider` that leverages Github Copilot
- [x] Github auth flow can be initiated from the settings UI
- [x] Modifies the `ILMProvider` interface to include an `IBrandingData`
interface, that allows a provider to specify how it wants certain
elements of the TerminalChat UI to look
- [x] Modified the various telemetry events to include the name of the
currently connected provider
## Validation Steps Performed
- [x] Auth flow works
- [x] Automatic refresh of the auth tokens works, meaning you don't need
to repeat the auth flow every few days
