Adds color update notification when setting lock screen live wallpaper

Fixes the issue where the customization hub preview did not change when
setting a lock screen-only live wallpaper for most cases. A follow-up CL
will address the case where wallpaper changes but colors do not.

Fixes: 277746962
Test: manually verified that change causes preview to update correctly
Change-Id: I6743c29abb778b184029bbca7d11c3aebd7a8bd4