For connect handlers that need to respond with a structured error or
structured object, pass an interface that hides the details of writing
an object to the response (error or runtime.Object).
Example use case:
Connect handler that accepts a body input stream, which it streams to a
pod, and then returns a structured object with info about the pod it
just created.
This change is required for the handler to work with sshtunnels.
Without it, `kubectl exec` and `kubectl port-forward` are broken
when an ssh proxy is used (see #9292). I manually verified this
fixes that issue, e2e test coming shortly.
Makes it possible to access the following subresources:
/namespaces/<ns>/pods/<pod-name>[:port]/proxy
/namespaces/<ns>/pods/<pod-name>/exec?container=<container>&command=<cmd>
/namespaces/<ns>/pods/<pod-name>/portforward
