Since meson 0.59.0, a feature object has an `allowed()`
method which returns true when the feature is set to
'enabled' or 'auto'.
Utilize that instead of the previously used
not feature.disabled()
Add system service and socket in addition to the user service and
socket. The system service is started as pipewire user and group and
clients need to be in the pipewire group to be able to connect.