Add media on lock screen setting

Add a new setting that controls whether media on lock screen is enabled,
disregarding the notifications status. The new setting is available
under media and privacy settings.

Bug: 229915240
Test: atest MediaHierarchyManagerTest
Test: atest KeyguardMediaControllerTest
Change-Id: I6adaa00ead1660488e4114d303c4394751ff87e8