[ECO-5193] Updated innner Message class

- Added missing fields for refSerial, refType and Operation

lib/src/main/java/io/ably/lib/types/Message.java

@@ -3,6 +3,8 @@
 import java.io.IOException;
 import java.lang.reflect.Type;
 import java.util.Collection;
+import java.util.Map;
+
 import com.google.gson.JsonArray;
 import com.google.gson.JsonDeserializer;
 import com.google.gson.JsonDeserializationContext;
@@ -74,6 +76,27 @@ public class Message extends BaseMessage {
      */
     public Long createdAt;
 
+    /**
+     * (TM2l) ref string – an opaque string that uniquely identifies some referenced message.
+     */
+    public String refSerial;
+
+    /**
+     * (TM2m) refType string – an opaque string that identifies the type of this reference.
+     */
+    public String refType;
+
+    /**
+     * (TM2n) operation object – data object that may contain the `optional` attributes.
+     */
+    public Operation operation;
+
+    public static class Operation {
+        public String clientId;
+        public String description;
+        public Map<String, String> metadata;
+    }
+
     private static final String NAME = "name";
     private static final String EXTRAS = "extras";
     private static final String CONNECTION_KEY = "connectionKey";