pipewire: install environment variable files

pipewire: install environment variable files

DISABLE_RTKIT saves us from nasty error messages about not being able
to connect to dbus. This doesn't make sense anyway, real-time mode
should not be enabled on embedded.

PIPEWIRE_DEBUG/G_MESSAGES_DEBUG are put there in comments so that
people can easily uncomment to figure out what is wrong with their
pipewire setup.

Bug-AGL: SPEC-2473

Change-Id: Id07d3d21f472885434158c300a227d53020c2189
Signed-off-by: George Kiagiadakis <george.kiagiadakis@collabora.com>