modules: refactor dbus reservation

The Dbus device reservation has been moved into a separate module, and has also
been refactored to allow reserving a device name before an actual device is
created. Devices now are created and destroyed by the monitor depending on
whether PipeWire owns the device or not. This also simplifies a lot the device
activation module to always enable devices when they are created, and never
worry about checking whether a device is acquired by PipeWire or not.