feat: create a starlight plugin that fetches module reference pages (#3)

[xynydev]

This approach works really surprisingly well.

Here's the reference page for rpm-ostree:

And here's the module.yml it was generated from:

name: rpm-ostree
shortdesc: The rpm-ostree module offers pseudo-declarative package and repository management using rpm-ostree.
description: |
  The [`rpm-ostree`](https://coreos.github.io/rpm-ostree/) module offers pseudo-declarative package and repository management using `rpm-ostree`.

  The module first downloads the repository files from repositories declared under `repos:` into `/etc/yum.repos.d/`. The magic string `%OS_VERSION%` is substituted with the current VERSION_ID (major Fedora version), which can be used, for example, for pulling correct versions of repositories from [Fedora's Copr](https://copr.fedorainfracloud.org/).

  Then the module installs the packages declared under `install:` using `rpm-ostree install`, it removes the packages declared under `remove:` using `rpm-ostree override remove`. If there are packages declared under both `install:` and `remove:` a hybrid command `rpm-ostree remove <packages> --install <packages>` is used, which should allow you to switch required packages for other ones.

  Note that [removed packages are still present in the underlying ostree repository](https://coreos.github.io/rpm-ostree/administrator-handbook/#removing-a-base-package), what `remove` does is kind of like hiding them from the system, it doesn't free up storage space.

  Additionally, the `rpm-ostree` module supports a temporary (waiting for `rpm-ostree` issue [#233](https://github.com/coreos/rpm-ostree/issues/233)) fix for packages that install into `/opt/`. Installation for packages that install into folder names declared under `optfix:` are fixed using some symlinks.

  ## Known issues

  When removing certain packages, some problem probably in upstream `rpm-ostree` causes a `depsolve` issue similar to below.
  \```
  Resolving dependencies...done
  error: Could not depsolve transaction; 1 problem detected:
  Problem: conflicting requests
  \```
example: |
  type: rpm-ostree
  repos:
    - https://copr.fedorainfracloud.org/coprs/atim/starship/repo/fedora-%OS_VERSION%/atim-starship-fedora-%OS_VERSION%.repo # when including COPR repos, use the %OS_VERSION% magic string
    - https://pkgs.tailscale.com/stable/fedora/tailscale.repo
  install:
    - python3-pip
    - libadwaita
  remove:
    - firefox
    - firefox-langpacks

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