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

@@ -18,6 +18,9 @@
 # This startup script is used only if PulseAudio is started in system
 # mode.
 
+.ifexists /data/override.pa
+.include /data/override.pa
+.else
 ### Automatically restore the volume of streams and devices
 load-module module-device-restore
 load-module module-stream-restore
@@ -45,3 +48,8 @@ load-module module-always-sink
 
 ### Enable positioned event sounds
 load-module module-position-event-sounds
+.endif
+
+.ifexists /data/custom.pa
+.include /data/custom.pa
+.endif