Motivation for this change

The current vim module is very limited, so only setting vim as the default editor is possible. This results in adding pkgs.vim to the systemPackages and setting the EDITOR environment variable.

However, if one wants to use a custom vim package, an overlay has to be created which is then used. If the same overlay definitions are used for multiple machines, it is not possible to configure different vim packages for different machines in a straight forward way.

This pull request adds a typical package option to the vim module to configure the vim package to be used.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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.