Add UI for multiple admins on Headless

In a series of CLs under topic add_ui_for_hsum_admins, UI and functionality for allowing multiple admins on HSUM build is added. In User settings and User switcher when creating a new user there is a new dialog prompting to choose admin status of the user to be created. In User details view there is a toggle that is visible to admin users that allows to modify admin status of existing users. This toggle is only applicable to full users that are not supervised, guests or a main device user.

Bug: 252790451
Test: croot && make RunSettingsRoboTests -j40 ROBOTEST_FILTER="com.android.settings.users.UserDetailsSettingsTest"
Change-Id: I34a6d223c009b7217e5e85077c886241ff06a2cb