A correctly configured AVAudioSession is needed on iOS to:
- allow the application to capture microphone audio (in some cases)
- avoid playback being silenced in silent mode
Without this, initializing AudioUnit for capture can fail on iOS >=17 (from my testing).
Since AVAudioSession has a lot of settings, in most cases its setup should be handled by the user/app.
However, just to have a basic default scenario covered, let's configure the bare minimum ourselves,
and allow anyone to disable that behaviour by setting configure-session=false on src/sink.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7856>
