Set FLAG_SILENT only for autogrouping updates

 - addAutogroupKeyLocked: only for forced grouped (app grouped) notifications
 - updateAutobundledSummaryLocked: when updating an autogroup summary

Flag: android.service.notification.notification_force_grouping
Test: atest NotificationManagerServiceTest

Bug: 408823758
Bug: 396573298
Change-Id: I709622182222ce5e59197a7af77080c20991a0a0