Changelog entries now use YAML files in changelog/unreleased/

[Robert Young]

Hi all!

We just switched to using logchange[1] for writing changelog entries and generating the CHANGELOG.md at release time. This will prevent merge conficts on the changelog during development.

If your PR modifies CHANGELOG.md, revert that change and add a YAML entry instead. DEV_GUIDE.md[2] covers the format and filename. After you merge main into your branch, 'mvn logchange:add' walks you through adding a log entry interactively. 

Note that the generator doesn't include all the possible fields that the logchange format supports yet, so stick to the ones in the dev guide.

1. https://logchange.dev

2. https://github.com/kroxylicious/kroxylicious/blob/main/DEV_GUIDE.md#changelog-entries

Thanks
Rob