JSON deserialization of non-JSON content in proxy-related methods

[philliphoff]

The generated methods for the proxy-related REST calls (e.g. ProxyGETNamespacedServiceWithHttpMessagesAsync()) expect responses to be JSON-serialized strings; this is often not the case (e.g. when a web site is being proxied and raw HTML, CSS, and JavaScript are returned).

Those proxy-related methods should probably just pass through the raw response content.

[brendandburns]

Yeah, this is tricky to do correctly. It will be improved when Port forwarding is supported.