Restrict callers for setSupervisionEnabledForUser

Callers are now restricted to the system and callers with
the BYPASS_ROLE_QUALIFICATION permission. This permission
is only granted to the SYSTEM_SHELL role holder.

Bug: 395630828
Flag: android.app.supervision.flags.supervision_manager_apis
Test: atest SupervisionServiceTest && atest CtsSupervisionTestCases
Change-Id: I4d045b2eff1521b33838bc330fe83ce6080017af