Enable Wireplumber Policy instance in ivi guest image.

Enable Wireplumber Policy instance in ivi guest image.

-add wireplumber-policy-config-agl recipe to guest, while
 wireplumber-config-agl remains in host.
-add packagegroup-pipewire-base which is needed by the policy recipe.
-mount host pipewire server socket in /var directory in guest image and
 define a PIPEWIRE_RUNTIME_DIR environment variable based on this new mount
 point.
-make the needed service file changes to have wireplumber policy
 instance start on its own with out depending on pipewire service, limit this
 change to lxc layers.
-install wireplumber@policy.service in sockets.targets.want directory,
 this is need for its self start, limit this change to lxc layers

Bug-AGL: SPEC-4100
Signed-off-by: Ashok Sidipotu <ashok.sidipotu@collabora.com>
Change-Id: Ifbd7a026c75a199bb540c1593d5a93f67a4bde02