Add ability to add custom PulseAudio startup commands

Loads two extra “user-configurable” configuration files:

/mnt/data/supervisor/audio/override.pa
… replaces the default configuration, if present.

/mnt/data/supervisor/audio/custom.pa
… is appended to the default configuration, if present.

Author: ntninja

rootfs/etc/pulse/system.pa

@@ -45,3 +45,7 @@ load-module module-always-sink
 
 ### Enable positioned event sounds
 load-module module-position-event-sounds
+
+.ifexists /data/custom.pa
+.include /data/custom.pa
+.endif