Log whether notification channel updates are user initiated

Bug: 124785950
Test: atest core/tests/coretests/src/android/service/notification
Test: (MANUAL):
      1. adb logcat -b events | grep sysui_multi_action
      2. Change priority of notification channel
      3. Observe event "757,856,..."

Change-Id: I34005c092290dd8bc5380f937a386e567dab38b0