Disconnect WebSocket connection on Session expiration as an event

[rwinch]

The first round of WebSocket support will check on each message to determine if the Session is still alive. This won't scale (particularly on outbound requests) well. Instead, we should detecting an Event of when the Session expires (#45) and then disconnect the WebSocket connection (depends on SPR-12288)

Depends On #45 SPR-12288 SPR-12314

[rwinch]

Fixed as part of #35