Add HAProxy Service Support

[MrHamel]

Hello!

As the title implies, I would like to see HAProxy support added in as a service. The reason for this request is, I do not know if the devenv services pages are simply pointing out viable services that can be easily setup in an environment by just referencing the standard Nix package + its configuration options, or special support must be added.

Thanks!

[Nebucatnetzer]

Special support needs to be added but the nixpkgs repo can certainly serve as an inspiration.
The existing services are defined here in case you want to try to set it up yourself: https://github.com/cachix/devenv/tree/main/src/modules/services

[domenkozar]

For inspiration see nixos module