SystemProperty to create disabled usertypes

For development, it helps to be able to create users whose usertype is
disabled or their limit has been reached.
We therefore introduce a system property for this.
It can only be used on debug builds.

Bug: 255793314
Bug: 137101239
Test: adb shell setprop debug.user.creation_override 1 && try to create disabled users
Change-Id: I6ab2aa80b0387b32f1b5fe5e9c8dd0096ed7bcd7