Communal Hub only for the main user

Test: atest CommunalInteractorTest
Test: verified that communal hub is disabled for a secondary user
Bug: 316961478
Fix: 316961478
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Change-Id: Iaf7a7f07b6cb9ae3afcc9c6fa3683b0480df752c