create github issues from server errors

@zeke and me have manually been pinging repo maintainers when their apps were hitting the wrong URLs or their assets weren't set up correctly. While we do now show more useful error messages, there's still a substantial amount of `>=400` http status codes.

Instead of doing manual work, we can automate this! 💻

Questions:

- [ ] which user to send this from (could be bot user but link @zeke and @juliangruber in the comment)
- [ ] should it be part of this service (+ realtime - coupling) or the monthly log aggregator?

Technical considerations:

- needs to wait a few calls before acting
- needs to keep track of which repo was already informed