Make HTTP request line limit configurable

### Required Terms

- [x] I agree to follow this project's [Code of Conduct](https://github.com/heroku/roadmap/blob/main/CODE_OF_CONDUCT.md)
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### What service(s) is this request for?

Heroku dynos

### Tell us about what you're trying to solve. What challenges are you facing?

In our application, we sometimes get very long URLs when our users filter data, and that can lead to the request line limit being exceeded. That results in a very confusing situation for our users, as the request will be dropped, and the generic error page that the browser shows does not make sense to them.

We want to control the limit in our own web server so that we can raise it to levels that are practically impossible for users to reach in our application.