Remove samples (#22288)

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

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

@@ -0,0 +1,63 @@
+package docs.cluster;
+
+import java.io.Serializable;
+
+//#messages
+public interface TransformationMessages {
+
+  public static class TransformationJob implements Serializable {
+    private final String text;
+
+    public TransformationJob(String text) {
+      this.text = text;
+    }
+
+    public String getText() {
+      return text;
+    }
+  }
+
+  public static class TransformationResult implements Serializable {
+    private final String text;
+
+    public TransformationResult(String text) {
+      this.text = text;
+    }
+
+    public String getText() {
+      return text;
+    }
+
+    @Override
+    public String toString() {
+      return "TransformationResult(" + text + ")";
+    }
+  }
+
+  public static class JobFailed implements Serializable {
+    private final String reason;
+    private final TransformationJob job;
+
+    public JobFailed(String reason, TransformationJob job) {
+      this.reason = reason;
+      this.job = job;
+    }
+
+    public String getReason() {
+      return reason;
+    }
+
+    public TransformationJob getJob() {
+      return job;
+    }
+
+    @Override
+    public String toString() {
+      return "JobFailed(" + reason + ")";
+    }
+  }
+
+  public static final String BACKEND_REGISTRATION = "BackendRegistration";
+
+}
+//#messages