Add healthcheck endpoint at /health

[Cellivar]

Thank you for building this app! I run it in a cluster environment which needs to be able to determine if it's up and running, and the usual pattern for this is to have a http://HOSTNAME/health endpoint that returns a 200 OK. Optionally it can contain some more information, though for this particular app just being online and serving requests is probably sufficient.

If you'd like I can whip up a basic PR to handle this case, basically a special case handling of the path that hardcodes /health to always short-circuit the request handler to return a 204 no content or something like that.