RealtimeAgent WebRTC

[davorrunje]

Why are these changes needed?

Currently, RealTimeAgent can stream audio from OpenAI API to a server and then to a client using WebSockets. This is not an optimal solution and streaming directly from OpenAI to a client using WebRTC is a much better solution.

This PR introduces the new OpenAIRealtimeWebRTCClient class that enables RealTimeClient to use WebRTC protocol.

Related issue number

Closes #390

Checks

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• I've added tests (if relevant) corresponding to the changes introduced in this PR.
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