Router request timeout

[snarfed]

I'd like to set a request timeout to limit starvation from runaway requests, particularly for the receive queue on the router service, which is serialized to one task as a time. I can't find an easy way or place to set a timeout though.

• App Engine Flex's service config has timeouts for the liveness and readiness checks, but not otherwise
• gunicorn's timeout setting only applies to sync workers, not the gthread worker we use
• Flask doesn't have anything, which makes sense

Maybe one problem is that there's (evidently) no clean way to kill a Python thread, especially such that the gthread thread poll will gracefully detect it and replace it with a new thread? Not sure.