Override Undertow's defaults so that the request URL of a forwarded request is spec-compliant and make it configurable via an application property

[wilkinsona]

By default, Undertow preserves the original request URL when a request is forwarded. This does not comply with the Servlet spec which states the following:

If this request has been forwarded using RequestDispatcher.forward(javax.servlet.ServletRequest, javax.servlet.ServletResponse), the server path in the reconstructed URL must reflect the path used to obtain the RequestDispatcher, and not the server path specified by the client.

We should override Undertow's default so that it's spec compliant and provide a configuration property so that users can easily restore the current behaviour if they are relying on it.