build(nix): create variant launch files

[quantum9Innovation]

This PR adds three variant launch files intended for testing a Nix migration in production:

• vehicle-nix-test runs all nodes that are confirmed to work locally with the Nix build system defined in https://github.com/ArcturusNavigation/arcturus_nix/
• vehicle-nix runs an additional node that should work on the robot, but will produce errors if run locally
• vehicle-non-nix should be run in parallel with vehicle-nix on the robot; it runs all nodes that do not run with the current Nix build infrastructure

[toyat522]

what if we create a branch called nix-build (or something like that) and that can be for nix builds. Theoretically, nothing should conflict, so we can just git pull origin main from nix-build when we want the latest code on nix-build. Then, you can push your nix-specific stuff to this branch, occasionally pulling from main.

[quantum9Innovation]

what if we create a branch called nix-build (or something like that) and that can be for nix builds. Theoretically, nothing should conflict, so we can just git pull origin main from nix-build when we want the latest code on nix-build. Then, you can push your nix-specific stuff to this branch, occasionally pulling from main.

Sounds good; the only issue would be that it might get a bit annoying to constantly merge the latest changes onto this branch. The Nix build files can actually be recreated with a simple command from the package.xml declarations, but the idea is to (eventually) switch to a Nix-based dependency management system (not that people would be forced to use this, but rather that it would act as an alternate dependency specification that is more complete/robust than the ROS package manifests), so the Nix package files should be an integral part of the codebase. Currently, however, it would not be entirely possible to build the entire project with Nix in a completely reproducible way, so I can just include a step in the Nix build process that rebuilds these files.

If you think this wouldn't disrupt the codebase at all, I think the best option would be to merge into main. Otherwise, if this might introduce too much confusion/technical debt, you can just close this PR and the arcturus-nix setup will still work fine.

[quantum9Innovation]

Wait nvm this is the PR for creating variant launch files, not package declarations. These files cannot be auto-generated, so the two options would be to keep this on a separate branch or merge into main. I would prefer merging into main, but this might add additional confusion and duplicate code, so if you think it would be better to put this on a separate branch for now, that's fine as well.

[quantum9Innovation]

@toyat522 @wellscrosby @JanelleCai ready for review; this doesn't change any of the main codebase but adds continuous integration using the Nix build system to check that every commit to main does not break any of the modules (can be extended to include more complex tests later). This PR also adds new launch files for testing purposes (doesn't affect existing launch files) and a pre commit hook for Nix users (shouldn't affect Docker workflow).