It's not really the responsibility of the session manager to load the
bluez5 device quirks, and it's easier for eg. Wireplumber if it doesn't
need to do it.
Move loading bluez-hardware.conf to be the responsibility of the bluez5
spa plugin, similarly as the alsa plugin deals with the ACP database.
Put the configuration to share/spa-0.2/bluez5, mirroring the plugin
directory structure in lib/spa-0.2/bluez5.