RBAModel: Added unknown_app content_id

RBAModel: Added unknown_app content_id

  Bug-AGL: SPEC-3738

Change-Id: I7b501696bdb7ec13abe67d07c0c29128d0068ee3
Signed-off-by: Anusha Gugale <external.agogale@jp.adit-jv.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25935
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Marius Vlad <marius.vlad@collabora.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit 275045b7acf6dc19dacd30e2254620b24feca993)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26007