Improve changelog generation

[karmaniverous]

Currently release-it uses auto-changelog to generate issue list from previous release.

This means if the previous release was a preview, then the next prod release carries notes from changes since the PREVIEW.

Notes should actually be from the last release at the same level, i.e. notes on release 3.0.0 should carry all commits since 2.0.0. ⬅️ IS THAT ACTUALLY A GOOD IDEA??

Also, the system should maintain a CHANGELOG.md file with a cumulative log of all changes, AND there should be some way of, uh, breaking out 🤓 breaking changes.

[karmaniverous]

Re Notes should actually be from the last release at the same level, that would make auto-changelog the wrong tool here because those notes are generated BEFORE the user chooses the release level.

[karmaniverous]

https://www.philipp-doblhofer.at/en/blog/automatic-changelog-and-versioning-with-git/