Disable swipe to communal hub when not available

Bug: 323065420
Fix: 323065420
Test: atest LockscreenSceneViewModelTest
Test: verified unable to swipe to CH after a reboot before unlocking
storage, and available again after unlocking
Flag: ACONFIG com.android.systemui.communal_hub STAGING
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT

Change-Id: I082bf6da99d923110d9d893c776963bcc374ed8e