On the service sisde, at the time of deserialization the unkwon elements from the client are
store in ExtensionDataObject.To send data to the client, the service has to serialize data into XML.
During this serialization process the data from ExtensionObjectOject is serialized into XML as it was
provided at the time of service call.
To use Extension object we need to make service class singleton by using ServiceBehavior attribute
ServiceBehavior (InstanceContextMode = InstanceContextMode.Single)