Bluetooth endpoints

Implements bluetooth endpoints and their creation. When a bluetooth device is connected, a source or sink bluetooth endpoint will be created (or both if the device supports both playback and capture). Each of these endpoints will have a "Multimedia" stream for A2DP profile or a "Call" stream for HSP/HFP profile (or both if the device supports both A2DP and HSP/HFP profiles). Profile switching is done automatically when one of the streams is enabled.

Very easy to test with the media-role option of pw-cat tool:

pw-cat -p file.wav --media-role "Multimedia"  # for A2DP
pw-cat -p file.wav --media-role "Call"        # for HSP/HFP