Make it possible to show text in time with the current spoken audio

[rohanliston]

When the conversational AI is speaking, I'd like to show a text transcript that updates in time with the audio being spoken. Currently, the onMessage callback only appears to provide the entire completed message without any timing data.

[PaulAsjes]

This can be tricky on the timing front as there might be a delta between receiving the transcript event and the audio event, but I've passed it along to the team.