RequestHeaderOriginalHost when Host is IP Address

Our application makes use of the Host header and so we use the `RequestHeaderOriginalHost` option in YARP. But there are certain healthcheck endpoints which get called by IP address and forwarding the IP Address as the Host header causes IIS to return a 400: `HTTP Error 400. The request hostname is invalid.`.

It would be helpful if the `RequestHeaderOriginalHost` option didn't copy the Host header if it was an IP address or there was an option for that behavior.