Deprecate the old way

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/public/Notification/IManager.php

@@ -53,6 +53,7 @@ interface IManager extends IApp, INotifier {
 	 * @param string $notifierService The service must implement INotifier, otherwise a
 	 *                          \InvalidArgumentException is thrown later
 	 * @since 17.0.0
+	 * @depreacted 22.0.0 use the IBootStrap registration context
 	 */
 	public function registerNotifierService(string $notifierService): void;