Used on the JAX-WS service implementation object to mark a method as preferring the 'async'
version of the method instead of the synchronous version. With JAX-WS, services default to the
synchronous methods that require the returning value to be returned from the method.
By marking a method with the @UseAsyncMethod annotation, if the transport supports it, CXF will call the async version that takes an AsynHandler object and the service can call that handler when the response is ready. If the transport does not support the CXF continuations, the synchronous method will be called as normal.