pipewire: use a conffile to autostart p-m-s

[CameronNemo]

It should be possible to disable autostart of pipewire-media-session and use some other method to start it, or start wireplumber instead.

Rather than patch /usr/share/pipewire/pipewire.conf, ship a drop-in config in /etc/pipewire/pipewire.conf.d and mark it as a conffile.

Testing the changes

• I tested the changes in this PR: YES