Show disabled add actions in COPE mode

Before this change these actions were hidden.

After this change, they are displayed but disabled which makes it more intuitive.

Bug: 336762423
Test: atest UserSettingsTest && atest UserDetailsSettingsTest
Flag: android.multiuser.new_multiuser_settings_ux
Change-Id: Ie07816b7d3817d12e78e1ec2692fcddea9328933