Adds the settings page that a user will reach from a mode settings page
when they tap on "App," to allow them to select whether all, none, or
priority modes can break through and send notifications.
Bug: 308819928
Bug: 331267485
Flag: android.app.modes_ui DEVELOPMENT
Test: build and test, controller unit tests
Change-Id: I5bcebfca0fc2882f839afdced8d2b817dad14e6c
