oniro-image-extra: Start graphics on boot

Currently oniro is using multi-user.target (systemctl get-default)

Relate-to: #789 (closed) Forwarded: https://gitlab.eclipse.org/eclipse/oniro-core/oniro/-/merge_requests?author_username=pcoval&scope=all&state=all Relate-to: eclipse/oniro-blueprints/vending-machine/meta-oniro-blueprints-vending-machine!2 (merged) Signed-off-by: Philippe Coval philippe.coval.ext@huawei.com