Add Realtime implementation

[StephenHodgson]

• https://openai.com/index/introducing-the-realtime-api
  • https://platform.openai.com/docs/api-reference/realtime-client-events
  • https://platform.openai.com/docs/api-reference/realtime-server-events
• https://github.com/openai/openai-openapi/issues/341

[davidmigloz]

For reference: https://github.com/openai/openai-dotnet/pull/238/

[StephenHodgson]

meh, for reference only. Not a fan of their implementation tbh.