ci: add generate-changelogs workflow

[piyoki]

Background

Add generate-changelogs workflow; it is identical to the one we have for daed;

Note: Only when we design and implement CI modularity, will we use a single unified workflow to generate changelogs for future releases.

Checklist

• The Pull Request has been fully tested
• There's an entry in the CHANGELOG
• There is a user-facing docs PR against https://github.com/daeuniverse/dae

Full changelogs

• ci: add generate-changelogs workflow
• chore(changelogs): add changelogs placeholder

Issue reference

As part of #156

[kunish]

We've already tested and verified this on daed, since the action is identical to the one daed is using, so it should be safe to assume this would work.