This change extracts the need for EstablishConnection to know about a
request's entire context. It also removes the concern of populating the
http.Response from EstablishConnection's responsibilities.
- extracted ResponseWriter from proxyConnection
- added bastion tests over websocket
- removed HTTPResp()
- added some docstrings
- Renamed some ingress clients as proxies
- renamed instances of client to proxy in connection and origin
- Stream no longer takes a context and logger.Service