Motivation for this change

My server is currently not starting, because the default sizes chosen by nginx are too small.
The problem is that you can only set the sizes before calling map the first time, and there is no configuration hook that allows for it before. That means I either have to replace the whole http section with my own, or do some ugly hacks by doing a "injection attack" in the upstreams config. Both of which I would love to avoid.

https://nginx.org/en/docs/http/ngx_http_map_module.html

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @