Implement the `DisableSupervisionActivity` for disabling supervision.

This activity allows the system supervision role holder to disable supervision on the device. It will respond to `DISABLE_SUPERVISION` intent.

It may be necessary to also delete make the activity delete the PIN in a followup.

Bug: 397687772
Flag: android.app.supervision.flags.supervision_manager_apis
Test: atest DisableSupervisionActivityTest
Change-Id: I63ed5079b1e77a08c26b9a40526a8378f2453647