pulseaudio: avoid to change volumes previously set

Because PulseAudio got flat-volumes on by default, getting an
echo-cancelled stream will, without option, set the master and
echo-cancelled volume to 33%.
This will make the user adjust their microphone every time.
Moreover, the module seems to re-adjust automatically the volume
with some gain control options.
So, in this patch, we load the echo-cancel without volume sharing
and with options to avoid to change a volume previously set.

Sources:
https://wiki.archlinux.org/title/PulseAudio/Troubleshooting
https://askubuntu.com/questions/1015327/disable-volume-auto-adjust-in-pulseaudio-module-echo-cancel
https://askubuntu.com/questions/279407/how-to-disable-microphone-from-auto-adjusting-its-input-volume

Change-Id: I981d1fedf7424895e6f44e9906e385f9c21bddee