Introduce a setting to enable/disable communal hub.

Bug: 314790871
Test: atest SystemUITests:CommunalRepositoryImplTest
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Flag: ACONFIG com.google.android.settings.flags.enable_glanceable_hub_setting DEVELOPMENT
Change-Id: Idcd43ee7e420a5165834fdf038ce22a4506c83e3
9 files changed