How to validate route configuration is correct

**We have talked about this in the past, but I can't find an issue for it. If there is an existing issue this one should be closed and duped against it**

Routes can be complicated in YARP, and mistakes in the routing configuration could allow for access to resources that should not be accessible without authentication/authorization etc. Operators of YARP proxies should have a way to be able to pass in URLs, headers etc., and validate what destination would receive the request, without having to rely on examining the response to validate the actual destination.