Airplay2

Support for Airplay2.

Just committing the patch from ckdo.

Did rebase and split into proper commits while retaining the original author.

If not appropriate I can set myself as an Author and mention ckdo that did the hard work in each commits.

It has been working well for me on my Sonos, both TCP & UPD, I even get lip sync if I set the proper latency in pactl. (2sec) Volume control from the hardware device is not working as DACP is not implemented in pulseaudio.

This superseeds https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/194 & https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/129