MDL-45641 event: Option to trigger user event manually

On some pages full user data is not stored before user_created/
user_updated event is triggred. So giving option to trigger that
manually, so it can be triggred after all data is saved
MDL-45641 event: unit test for optional user_created/updated event trigger
MDL-45641 core_user: relateduserid not needed in user_created/updated event