Add setting for promoted (live) notifications

Add a switch to control whether live notifications are permitted for an app, at the top of the app's notification settings page. This controls canPostPromotedNotifications() for that app.

Bug: 369150427
Flag: android.app.ui_rich_ongoing
Test: manual, PromotedNotificationsPreferenceControllerTest
Change-Id: I3a7c05721f1e879fb5fb0f5fb5f283dedbd195da