npm: add module

[mirkolenz]

Description

Add module for configuring .npmrc via home manager. Inspired by the NixOS module.

I'm not sure if the tests are set up correctly. Since the package is a nested attrset, I didn't use a stub, but set the package to null instead. Please let me know if there's a better way to handle this.

Checklist

• Change is backwards compatible.

• Code formatted with nix fmt or
  nix-shell -p treefmt nixfmt deadnix keep-sorted --run treefmt.

• Code tested through nix run .#tests -- test-all or
  nix-shell --pure tests -A run.all.

• 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.
  • Generate a news entry. See News
  • Basic tests added. See Tests

• If this PR adds an exciting new feature or contains a breaking change.

  • Generate a news entry. See News

[mirkolenz]

OK, I think I found an elegant solution: I created a custom ini generation function which automatically appends square brackets to list values. I renamed the option from npmrc to settings with a proper type and updated the tests by adding an array-based entry.

One thing I changed as well compared to the last iteration: The package option now installs the nodejs package because at least on my system, using pkgs.nodePackages.npm or pkgs.nodejs.pkgs.npm resulted in a full rebuild of the nodejs package (which is expensive). It also seems to be the case that pkgs.nodePackages_xx is no longer available and just not updated in the upstream NixOS module.

Let me know what you think 😄