Added new overlay property config_enableMainUserPermanentAdmin

config_enableMainUserPermanentAdmin overlay property is added to
decide the main user removal behaviour on different form factors.

If config_enableMainUserPermanentAdmin is true the main user can't be
deleted or downgraded to non-admin status.

Bug: 262368967
Test: NA
Change-Id: If2102fc6333f170c73160aad068f8cd7df003749