Repository transfer has to be confirmed, if user can not create repo for new owner (#14792)

* make repo as "pending transfer" if on transfer start doer has no right to create repo in new destination

* if new pending transfer ocured, create UI & Mail notifications

modules/notification/notification.go

@@ -290,3 +290,10 @@ func NotifySyncDeleteRef(pusher *models.User, repo *models.Repository, refType,
 		notifier.NotifySyncDeleteRef(pusher, repo, refType, refFullName)
 	}
 }
+
+// NotifyRepoPendingTransfer notifies creation of pending transfer to notifiers
+func NotifyRepoPendingTransfer(doer, newOwner *models.User, repo *models.Repository) {
+	for _, notifier := range notifiers {
+		notifier.NotifyRepoPendingTransfer(doer, newOwner, repo)
+	}
+}