Store release information in public

[matsduf]

Purpose

Add release information to the public document path. This PR is not to be merged. It is to show a proposal that would be executed at an upcoming release for that release.

File "public/RELEASE.md" is added. The file should be updated at release time with the release information of the latest release (and not including previous releases). The content is to be directly copied to the Github release page, e.g. https://github.com/zonemaster/zonemaster/releases/tag/v2023.2.1. No edits should be needed.

SUMMARY.md has also been updated with a link to the RELEASE.md file.

I built a "book" and the file works well into the book.

How to test this PR

Review. Build a "book" following the instruction in https://github.com/zonemaster/zonemaster?tab=readme-ov-file#documentation.

[mattias-p]

This looks really nice.

Perhaps rename RELEASE.md to RELEASES.md and keep a history of all releases in the same file, or of all releases up to a certain point (e.g. v2023.2.1 and newer). I'm not sure if there's huge value in this but it just feels a bit weird to me to remove the details of the last release every time we make a new one.

[matsduf]

My idea is exactly to keep only the latest release notes in the file, and refer to Github release notes for previous releases. Then the content will be exactly the same as is entered in Github, and the focus will be on the latest release.

[mattias-p]

Fair enough, I reckoned as much. I had a different idea and I wanted to raise it.

[matsduf]

This PR will not be merged. It will be used as model at release time.

@tgreenx and @mattias-p, please review again.