OZG-7573 OZG-7991 Call on*()-methods on requestObserver

vorgang-manager-server/src/main/java/de/ozgcloud/vorgang/vorgang/redirect/EingangForwarder.java

@@ -47,9 +47,9 @@ class EingangForwarder {
 						.thenCompose(ignored -> sendRepresentations(representations))
 						.whenComplete((result, ex) -> {
 							if (ex != null) {
-								responseObserver.onError(ex);
+								requestObserver.onError(ex);
 							} else {
-								responseObserver.onCompleted();
+								requestObserver.onCompleted();
 							}
 						})
 		);