WIP: Align changelog format with other GitLab components
CHANGELOG is renamed to CHANGELOG.md and versions are now an h2 markdown tag.
This is the syntax in use on all the other components, and it's essential for release-tools. With this syntax, it will be able to inject a new release changelog in the right position.
This conversion was generated by the following shell command
sed -E 's/^v? ?([0-9]+\.[0-9]+\.[0-9]+)/## \1/' CHANGELOG > CHANGELOG.md
Edited by Alessio Caiazza (OOO until 2024-08-26)