provide a stream to listen for both recording and playback

[ukrx-xamd]

Currently there is a StreamController for Volume playback - presumably this is to display some type of audio graph as a user records a message. It would be great also to have the ability to subscribe to a recordSubscription and a playSubscription so that the flutter client can listen on these streams and provide some additional UI feedback - use case -> To display a playback / record duration which constantly ticks as the audio is recorded or played back.