Releasing 2.0.0-alpha.4 (#5279)

* Version bump

* Split generate_changelog.sh into separate script

Can be run in the format `generate_changelog.sh $previous_version $version`.

* remove early exit from publish_draft_release.sh

* adding changelog

* ci: change last_github_release to also find pre-releases

Co-authored-by: Martin Pugh <[email protected]>