return transport defined response on subscription updates just like on new registrations

lib/Dav/SubscriptionManagementPlugin.php

@@ -169,6 +169,7 @@ class SubscriptionManagementPlugin extends ServerPlugin {
 						[
 							'success' => $updateSuccess,
 							'errors' => $updateErrors,
+							'response' => $responseContent,
 						] =	$transport->updateSubscription($subscription->getId(), $subscriptionOptions);
 
 						if(!$updateSuccess) {

lib/PushTransports/WebPushTransport.php

@@ -111,6 +111,7 @@ class WebPushTransport extends Transport {
 		// there are no options which can be edited -> NOOP
 		return [
 			'success' => True,
+			'response' => "",
 		];
 	}
 }