[DAB RBAC] Re-implement system auditor as a singleton role in new system (#14963)

* Add new enablement settings from DAB RBAC

* Initial implementation of system auditor as role without testing

* Fix system auditor role, remove duplicate assignments

* Make the system auditor role managed

* Flake8 fix

* Remove another thing from old solution

* Fix a few test failures

* Add extra setting to disable custom system roles via API

* Add test for custom role prohibition

awx/main/access.py

@@ -652,7 +652,6 @@ class UserAccess(BaseAccess):
                 User.objects.filter(pk__in=Organization.accessible_objects(self.user, 'read_role').values('member_role__members'))
                 | User.objects.filter(pk=self.user.id)
                 | User.objects.filter(is_superuser=True)
-                | User.objects.filter(profile__is_system_auditor=True)
             ).distinct()
         return qs