[devel-noble] provide a way for ports to provide additional parameters for pa-modules-droid (via Deviceinfo preferably)

Because !48 (merged), any port that overlay touch.pa would have to update it with a new copy. But rather than let ports doing that, let's eliminate the reason for ports to do that.

Have a code that read a Deviceinfo property, then inject it as an environment variable in Systemd. pulseaudio-module-droid-discover could then pick it up and inject it into pulseaudio-module-droid-NN's module arguments. Preferably pulseaudio-module-droid-discover shouldn't link into Deviceinfo to keep it useful outside of Ubuntu Touch ecosystem.

Combined with ubports/development/core/hybris-support/pulseaudio-module-droid-discover!6 (merged) this should remove the need for porters to overlay touch.pa.