jibri: switch to PulseAudio

Using PulseAudio means no longer needing to mount /dev/snd/ which should
make deploying Jibri much easier.

Credits:

https://github.com/openfun/jibri-pulseaudio
https://community.jitsi.org/t/tip-pulseaudio-support-for-jibri/65780
https://github.com/kpeiruza/jitsi-images

jibri/rootfs/home/jibri/.config/pulse/default.pa

@@ -0,0 +1,8 @@
+.include /etc/pulse/default.pa
+
+# Load the virtual sink and set it as default
+load-module module-virtual-sink sink_name=jibri-loop
+set-default-sink jibri-loop
+
+# set the monitor of the jibri-loop sink to be the default source
+set-default-source jibri-loop.monitor