Adds group to DND settings if channel names same

Adds the channel group name as a summary to the DND channel Preference if two
or more channels have identical names in the DND Menu. This allows users to
disambiguate between the channels.

Bug: 294333850
Test: Unit test updated, run with $make -j RunSettingsRoboTests ROBOTEST_FILTER=AppChannelsBypassingDndPreferenceControllerTest
Change-Id: I4eaf48e5b2ea6513098fde79c3f81d18c6f4bb3d