Switch to 'Keep a Changelog' to maintain changelogs

[avivace]

See: https://keepachangelog.com/en/1.1.0/

[Rangi42]

This looks very similar to how we already structure our changelogs, with Added, Changed, and Removed headings, bullet-pointed changes, ISO-formatted dates, and (obviously) change descriptions written for the users, not just copy+pasting our Git commit messages. Unlike their example, we put deprecations/removals on top, but I think that's more in tune with their own advice: "If you do nothing else, list deprecations, removals, and any breaking changes in your changelog."

I also don't see any mention of keepachangelog on Discord that would provide context for why/where this suggestion is coming from.

@avivace Can you explain what you/we should do to resolve this issue?

[avivace]

Our changelogs are already very close to the Keep a Changelog format. The goal here isn't a big overhaul: it would be a relatively minor effort to smooth over the remaining formatting differences and fully align with the spec (retroactively).

The main motivation beyond this adoption and the committment to future consistency is machine-readability: a strictly formatted changelog can be parsed automatically, which would allow us to e.g. collect and publish release notes programmatically and feed them into other tooling (e.g. to docusaurus in rgbds-www).

We could add a CI pipeline step to validate the format and keep things tidy going forward (I have had a very good experience with https://github.com/cyberark/parse-a-changelog )