Assure intercept methods to not change the message

This was done by cloning.

parser_commons/src/main/java/org/eclipse/moquette/proto/messages/ConnectMessage.java

@@ -164,4 +164,12 @@ public class ConnectMessage extends AbstractMessage {
         }
         return base;
     }
+
+    public ConnectMessage readOnlyClone() {
+        try {
+            return (ConnectMessage) super.clone();
+        } catch (CloneNotSupportedException e) {
+            return null;
+        }
+    }
 }

parser_commons/src/main/java/org/eclipse/moquette/proto/messages/PublishMessage.java

@@ -54,4 +54,14 @@ public class PublishMessage extends MessageIDMessage {
     public void setPayload(ByteBuffer payload) {
         this.m_payload = payload;
     }
+
+    public PublishMessage readOnlyClone() {
+        try {
+            final PublishMessage clone = (PublishMessage) super.clone();
+            clone.m_payload = this.m_payload.asReadOnlyBuffer();
+            return clone;
+        } catch (CloneNotSupportedException e) {
+            return null;
+        }
+    }
 }