community/bluez-alsa: add conf.d configuration file

bluealsa 4 does not enable any BT profile by default and will crash if none are set
https://github.com/Arkq/bluez-alsa/commit/b9f72d6a335dee3fcd6ed4467a31b1ce83948306

We add conf.d file to allow setting profiles and other options. Profiles a2dp-source and a2dp-sink are enabled, as per default systemd service
https://github.com/Arkq/bluez-alsa/commit/32c55bde2f100a2c0d62858716f5ff208fa43ab8