[Feature request] Allow adding custom classic nix packages #2717
Description
What problem are you trying to solve?
I have packaged something that is outside of nixpkgs the same way nixpkgs packages stuff and would like to use it in devbox. Unfortunately, it seems like only flakes are available, which is a pity as a good chunk of things don't use flakes and are in a state (unmaintained or otherwise) where they won't. Additionally there is no official flakes documentation besides nix.dev which explains the concept and its status as an experimental feature but cannot function as documentation (it's a single page linking out to a few blog posts and community posts).
What solution would you like?
The ability to add something like "nix:./my-package.nix" to the packages in devbox.json and for that to be called by pkgs.callPackage. Something that simple would allow custom packages to added without depending on or knowing about flakes and all its intricacies.
Alternatives you've considered
devbox documentation that explains how the flake integration works, because then maybe I could understand it and hack it to use non-flakes.