Set http payload limit by regex

[coccyx]

We should allow setting the payload size limit by matching the payload against a regex. This way, if you have endpoints or patterns you know you want unlimited payload size, you can match them by regex.

This needs some investigation, especially with HTTP/2, whether there's a simple heuristic to be able to match a regex in the middle and understand a single HTTP event with boundaries.

[iapaddler]

We probably want to limit payload volume in general, beyond HTTP. Reference issue #458.