.github: Add a "Module requests" issue template

---

name: Module requests

about: For NixOS modules that you would like to see

title: 'Module request: MODULENAME'

labels: '9.needs: module (new)'

assignees: ''

---

### Description

<!-- Describe what the module should accomplish: -->

### Notify maintainers

<!-- If applicable, tag the maintainers of the package that corresponds to the module. If the search.nixos.org result shows no maintainers, tag the person that last updated the package. -->

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Note for maintainers: Please tag this issue in your PR.

---

Add a :+1: [reaction] to [issues you find important].

[reaction]: https://github.blog/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/

[issues you find important]: https://github.com/NixOS/nixpkgs/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc