Monitoring for CodeWorld game server

It would be good to get more visibility on what's happening inside the CodeWorld game server.

For the main web server, the current state is not so bad, for a few reasons: (a) the site is fundamentally pretty simple, (b) all useful work spawns subprocesses for GHCJS and writes artifacts with timestamps, and (c) there are logs, at least. None of these things, though, are true of the new game server. I'd like to know how many concurrent sessions and connections it's maintaining, how long-lived they are, whether there are leaks over time, the distribution of session sizes, the rate of messages relayed, etc. None of these are visible in the current setup.