[bug#39053] [PATCH] Add pulseaudio configuration and fix volume bugs

[Leo Prikler]

This series of patches adds a configuration type for pulseaudio and also fixes
a bug, where various applications would inadvertently max out the system volume
(see e.g. #38172).

The second patch of this series differs from the one proposed there, in that
it uses environment variables to achieve its goal rather than rebuilding
pulseaudio.  As a result, pulseaudio-service will very likely ignore user
configuration in $XDG_CONFIG_DIR/pulse unless those variables are unset.
Doing so in ~/.profile or an equivalent to it should suffice.

Regards,
Leo