Allow TestHarness exemption from forced grouping notifications

 Forced grouping for all notifications in Test Harness can be disabled via ADB cmd:
 - adb shell cmd notification set_exempt_th_force_grouping true

 While running tests in Test Harness mode, disable forced grouping of abusive notifications:
 	- group summary notifications without children
 	- group child notifications without summary

 Autogrouping of ungrouped notifications is still enabled.

Flag: android.service.notification.notification_force_grouping
Test: atest PlatformScenarioTests:android.platform.test.scenario.notification

Bug: 359340654

Change-Id: Iaa74d9d5d3b338b68d3201f8f96854cd72f19a2c