JobScheduler: Update the media backup exemption policy.

High priority jobs from cloud media package will be
exempted and elevated to the WORKING_SET bucket for
more quota in applying the standby bucket throttling.

Bug: 436531976
Test: atest
FrameworksMockingServicesTests:com.android.server.job.controllers.JobStatusTest
Flag: com.android.server.job.update_media_backup_exemption_policy

Change-Id: I4aa64119f18453305c8c835c216fafc62bd353ac