WS should use Ingress-domain

[Edward13ruf]

The WS config should use Ingress-domain when returning the URL. Currently when a user asks for a websocket transport, the hostname they are connecting to the server with is used to populate the WS url. This can lead to very awkward errors when using loadbalancers or reverse proxies. The WS URL should not rely on anything userspecified, but should instead be entirely derived from server config.

[fredriklindberg]

The HTTP listener constructs the base url from the incoming request to work out of the box in the majority of the cases.
If the reverse proxy/load balancer injects the correct forwarded headers the constructed url should work. There is currently no way to override the base url.

The API can be restricted to only be available on a specify URL by specifying --api-url.