chore: add commit and issue links to changelog

[eljamm]

I took inspiration from git-cliff's own configuration and added commit and issue links to the changelog. For example:

### Overview

- Add button to link examples' docs ([#1280](https://github.com/ngi-nix/ngipkgs/issues/1280)) - ([16692b4](https://github.com/ngi-nix/ngipkgs/commit/16692b4ab4fbf70be91d5ac51cf4de924000b5f5))
- Add code-snippet and demo content-types - ([5278d1a](https://github.com/ngi-nix/ngipkgs/commit/5278d1a2a27c2bfb6cddb6d40f9dff1941c2bbf2))
- Modularize demo instruction - ([5474ca3](https://github.com/ngi-nix/ngipkgs/commit/5474ca3369debde2d09ead73460eab64608cc893))

This also adds a comparison between the tags and the ones preceding them:

## [25.12](https://github.com/ngi-nix/ngipkgs/compare/25.11..25.12) - 2026-01-12

### Bug Fixes

- *Canaille:* Disable tests; mark unbroken - ([a1e5e27](https://github.com/ngi-nix/ngipkgs/commit/a1e5e27b51d681d364ecb9b8b622311c059cf027))

To see how this would look like, check out this file.