Adds configurable output format for ElevenLabs TTS, allowing users to
override the default mp3_44100_128 format.
This is useful for channels like WhatsApp that require specific audio
formats (e.g., 24kHz, 48kbps, mono) that differ from the defaults.
Changes:
- Add outputFormat field to elevenlabs config in types.tts.ts
- Add outputFormat to zod schema validation
- Use configured outputFormat in tts.ts, falling back to channel defaults
- Infer file extension from custom outputFormat when specified
Example config:
messages.tts.elevenlabs.outputFormat: "mp3_22050_32"
