MULE-8018: Merge http connector code cleanup

I don't understand this comment, isn't the idea of using the interface to then program to the interface and decouple from the implementation, but if interface doesnt have methods, you end up needing to use the implementation directly.
This can be seen in your implementation where you have org.mule.module.http.api.listener.HttpListenerBuilder#setListenerConfig but then cast down to DefaultHttpListener! IMO you either need to recieve the concrete implementation here (which kind of renders the interface pointless doesn't it?) or add the required get methods to the interface..