Allow disabling framework Backup scheduling

This remerges ag/20838898 that was reverted due to breaking a
robolectric test in BackupFrameworksServicesRoboTests.

Test: 1. atest BackupFrameworksServicesRoboTests
      2. atest CtsBackupHostTestCases
Bug: 259953764
Change-Id: I11c7dbe9959f5b5d1acf53e7830b7256357768e2
15 files changed