fix: OctopusImpl forgot register listener reference init + first message register

Author: julian-siebert

plugin/src/main/java/studio/o7/octopus/plugin/OctopusImpl.java

@@ -78,6 +78,14 @@ public void onCompleted() {
             }
         });
 
+        requestRef.set(observer);
+
+        observer.onNext(ListenMessage.newBuilder()
+                .setRegister(ListenRegister.newBuilder()
+                        .setKeyPattern(listener.getKeyPattern())
+                        .setPriority(listener.getPriority())
+                        .build()).build());
+
         this.listeners.put(listener.getListenerUniqueId(), new Pair<>() {
             @Override
             public Listener left() {