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/defaults/jibri.conf

@@ -103,14 +103,10 @@ jibri {
 
     ffmpeg {
       resolution =  "{{ $JIBRI_RECORDING_RESOLUTION }}"
-      {{ if .Env.JIBRI_FFMPEG_AUDIO_SOURCE -}}
       // The audio source that will be used to capture audio on Linux
-      audio-source = "{{ .Env.JIBRI_FFMPEG_AUDIO_SOURCE }}"
-      {{ end -}}
-      {{ if .Env.JIBRI_FFMPEG_AUDIO_DEVICE -}}
+      audio-source = "pulse"
       // The audio device that will be used to capture audio on Linux
-      audio-device =  "{{ .Env.JIBRI_FFMPEG_AUDIO_DEVICE }}"
-      {{ end -}}
+      audio-device =  "default"
     }
 
     {{ if .Env.CHROMIUM_FLAGS -}}