Add option for clients to forward requests from the host IP to 127.0.0.1

If some services listens to localhost instead of the node's FQDN/public ip, it's currently not possible for the client to scrape their metrics.

This feature is already implements in the [Rancher's PushProx fork](https://github.com/rancher/PushProx/blob/e47d7474858a6b3ca3938cf41c0706ac94c30651/cmd/client/main.go#L54)