Introduces a new TTS provider using Google Cloud Text-to-Speech (Chirp HD model). This allows for higher quality and more natural-sounding voice synthesis.
The `TTSProviderCog` now includes:
- A `google_cloud_tts` option in the `_synthesize_speech` method.
- Checks for the `google-cloud-texttospeech` library and provides installation instructions if missing.
- Error handling for common Google Cloud TTS issues like quota limits or credential problems.
- A new choice in the `/ttsprovider` slash command for "Google Cloud TTS (Chirp HD)".
- A check for the availability of the `google.cloud.texttospeech` module on startup.
