Add glow

[m-vz]

Description

Add Glow, a terminal-based markdown reader.
As this is my first contribution to home-manager, feel free to correct me on any mistakes I made.
This supercedes and closes #2332.

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

[m-vz]

Hmm apparently there's some duplicate maintainers... I'm guessing these shouldn't be removed in this PR...?

[m-vz]

Turns out I didn't realise lib.hm.maintainers and lib.maintainers aren't the same thing.