distrobox: add module

[aguirre-matteo]

Description

Added programs/distrobox.nix module. It provides the option "programs.distrobox.containers", which makes it possible to declare a list of containers to be created. Since building those containers is not possible at build time (because none container backend is available at that time), I also added the options "enableBashIntegration" and "enableZshIntegration", which adds some code to .bashrc and .zshrc respectively that looks for changes in the file "containers.ini" and prompts the user to build the containers.

Support for other shells, like Fish and Nushell, will be added soon.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all
  or nix build --reference-lock-file flake.lock ./tests#test-all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

[aguirre-matteo]

Support for Fish and Nushell has been added. So the pull request is ready to be merged.