Changed behavior of HsumBootUserInitializer to "ramp-up" a config.

This change will allow devices disabling the main user to be ramped
up by a flag (create_initial_user), even after they changed
config_designateMainUser (from true to false)

Bug: 402486365
Test: atest FrameworksMockingServicesTests:HsumBootUserInitializerDesignateMainUserOnBootTest
Flag: android.multiuser.create_initial_user

Change-Id: I866d20b9356976e922168e41968a1a8dd56189f6