[MM-34179] app: move cluster registeration to server creation (#17306)

* app: move cluster registeration to server creation

* initserver via fakeapp

* reflect review comments

app/server.go

@@ -454,6 +454,7 @@ func NewServer(options ...Option) (*Server, error) {
 	})
 
 	if s.joinCluster && s.Cluster != nil {
+		s.registerClusterHandlers()
 		s.Cluster.StartInterNodeCommunication()
 	}