Add boot user override id to its own label

Define a new label for android.car.systemuser.bootuseroverrideid so that
partners can write to the system property during the boot sequence.

Bug: 130297788
Test: Add a set_prop call to a .te file and check to ensure the context
and type was defined by running "m -j".

Change-Id: Ie286697ab1d4f1ba8ead5056d158695e9ec42aef
(cherry picked from commit aa61a0a1c17ec27c6d483920925661f5fa4ab67e)
2 files changed