Disable PS entry point and Activity when PS is not allowed.

In this change we disable:
1. Security Center Entry point
2. PrivateSpaceAuthenticationActivity

when private profile is not present and cannot be added.

Additionally, the intent exposing PrivateSpaceAuthenticationActivity
is also non-exported and changed to a better name.

Bug: 328578044
Test: Manual build and flash
Change-Id: I13d298316c6d719d0b06e4969989ea1da83dd4c6