adding ack method to Message interface (apache#1627)

* adding ack method to Message interface

* adding ack to have default implementation

* adding fail method

* correcting grammar

* removing unneccesary colon

pulsar-connect/core/src/main/java/org/apache/pulsar/connect/core/Message.java

@@ -40,4 +40,14 @@ public interface Message<T> {
      * @return The message data
      */
     T getData();
-}
+
+    /**
+     * Acknowledge that this message is fully processed
+     */
+    default void ack() {};
+
+    /**
+     * To indicate that this message has failed to be processed
+     */
+    default void fail() {};
+}