Remove samples (#22288)

Add code, that was used for documentation to the appropriate projects
or akka-docs.

akka-docs/rst/java/code/docs/cluster/TransformationFrontend.java

@@ -0,0 +1,48 @@
+package docs.cluster;
+
+import static docs.cluster.TransformationMessages.BACKEND_REGISTRATION;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import docs.cluster.TransformationMessages.JobFailed;
+import docs.cluster.TransformationMessages.TransformationJob;
+import akka.actor.ActorRef;
+import akka.actor.Terminated;
+import akka.actor.UntypedActor;
+
+//#frontend
+public class TransformationFrontend extends UntypedActor {
+
+  List<ActorRef> backends = new ArrayList<ActorRef>();
+  int jobCounter = 0;
+
+  @Override
+  public void onReceive(Object message) {
+    if ((message instanceof TransformationJob) && backends.isEmpty()) {
+      TransformationJob job = (TransformationJob) message;
+      getSender().tell(
+          new JobFailed("Service unavailable, try again later", job),
+          getSender());
+
+    } else if (message instanceof TransformationJob) {
+      TransformationJob job = (TransformationJob) message;
+      jobCounter++;
+      backends.get(jobCounter % backends.size())
+          .forward(job, getContext());
+
+    } else if (message.equals(BACKEND_REGISTRATION)) {
+      getContext().watch(getSender());
+      backends.add(getSender());
+
+    } else if (message instanceof Terminated) {
+      Terminated terminated = (Terminated) message;
+      backends.remove(terminated.getActor());
+
+    } else {
+      unhandled(message);
+    }
+  }
+
+}
+//#frontend