Add @SystemApi annotation to the ENABLE and DISABLE_SUPERVISION intent actions...

Add @SystemApi annotation to the ENABLE and DISABLE_SUPERVISION intent actions to allow system apps to use the constant.

Bug: 421268765
Bug: 390242232
Flag: android.app.supervision.flags.supervision_manager_apis
Test: EXEMPT not applicable
Change-Id: Ib6d41634986703de422e941d8d534069052b064c