Add API to allow controlling proxying connections to controllers and routers.

[plorenz]

The following attributes will be added to the SDK Config struct:

	//Allows providing a function which controls how/where request to a controller are proxied.
	//See [http.Transport.Proxy] for more information
	//If this value is nil, [http.ProxyFromEnvironment] is used. If you never want a proxy to be used,
	//set a function which always returns nil.
	CtrlProxy func(*http.Request) (*url.URL, error)

	//Allows providing a function which controls how/where connections to a router are proxied.
	RouterProxy func(addr string) *transport.ProxyConfiguration