Add demo specific KUKSA.val configuration

Add demo specific KUKSA.val configuration

Add kuksa-val-agl and kuksa-val-agl-demo-cluster recipes that install
extra configuration for KUKSA.val for the AGL demo platform.

Changes:
- Add kuksa-val-agl recipe to install AGL specific signals overlay
  and uses a new environment variable hook in the kuksa-val systemd
  unit to pass the required --overlays option to pick it up.
- Add kuksa-val-agl-demo-cluster recipe to install cluster support
  specific kuksa-val environment file that makes kuksa-val-server
  listen on all addresses.  This is hopefully a stop gap approach
  for the cluster demo until support for listening on multiple
  addresses is added upstream.
- Add kuksa-val-agl to packagegroup-agl-ivi-services to enable the
  AGL specific signals in the demo images.
- Add kuksa-val-agl-demo-cluster to packagegroup-agl-demo-cluster-support
  to pick it up when the agl-demo-cluster-support feature is used
  to build an image for the full AGL demo setup.

Bug-AGL: SPEC-4405

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I41e90829a40aebf7f29e7719334f37d639542e07