StreamReceiver for receiving incoming data stream
To receive upload from the client we need to register a StreamReceiver that
will get a URL that will handle receiving of an upload stream.
For creating a StreamReceiver we first need to create a StreamVariable that
handles terminal Upload monitors and controls the upload during the time it
is being streamed.
Then the stream can be registered through the Element API.
StreamReceiver streamReceiver = new StreamReceiver(
getElement().getNode(), "upload", getStreamVariable());
getElement().setAttribute("target", streamReceiver);