Add a new exemption for backup-related jobs.

Apps who have the new RUN_BACKUP_JOBS permission will be allowed to run
longer backup-related jobs by the means of elevating their bucket if
necessary. This new behavior is similar to the cloud media provider
exemption.

Bug: 318731461
Test: atest JobStatusTest
Change-Id: I4432eec8637b71e71dcecd74740a592399649c70