Change the signature from metadata to preference key, so that the API
could be used to notify other preferences on the same screen.
NO_IFTTT=Catalyst only
Bug: 332201912
Flag: com.android.settings.flags.catalyst
Test: atest
Change-Id: Ibdf5f9004471d5491a0be1e84365cbe9f136c373
Add the skeleton of the Data Saver
Bug: 368359883
Test: atest DataSaverScreenTest
Flag: com.android.settings.flags.catalyst_restrict_background_parent_entry
Change-Id: I008c1ff7a1ad4ff1eeb95be730680abe5666f26c