MPRIS

[danirabbit]

Problem

Document how media apps can integrate with the sound indicator and media keys

Proposal

The GNOME MediaKeys interface is deprecated, but MPRIS apps can be controlled with media keys, so better to implement MPRIS anyways.

Prior Art (Optional)

I now have a fairly clean MPRIS implementation in Music that could be used for modeling docs after: https://github.com/elementary/music/tree/main/src/DBus