Add support for Elevenlabs and other realtime voice providers

[rohanprichard]

Hi! Just tested out this project, and it looks great. Having an agent be able to join calls, explain itself and more adds a whole new level of realism.

I was wondering if there are any plans to integrate Elevenlabs, Gemini realtime, etc providers, in order to improve the quality of audio being generated, to make it sound more natural. The webpage-av docs and the voice-agent template already point toward a BYO Voice AI system, so I guess it falls in line with your path.

Happy to raise a PR with the changes to use Elevenlabs as a TTS replacement initially, and to chat about further ideas!

[jomon003]

We are currently testing the realtime expressive voice along with a bit more integrations that just the ability to talk. Expecting to release in a week or two.