AudioTranscription has non-existing enabled field

[ysimonson]

For the realtime types, AudioTranscription currently has an enabled field, but the API does not have this. This triggers an error when trying to set an audio transcription on session update:

called `Result::unwrap()` on an `Err` value: invalid_request_error [code=Some("unknown_parameter"), param=Some("session.input_audio_transcription.enabled")]: Unknown parameter: 'session.input_audio_transcription.enabled'.

[codesoda]

This is addressed in #391

[ysimonson]

Yeah I also opened a PR to fix but it never got attention. Not sure if this is a priority.