[prep-release-3.1.0-a3] Update version to 3.1.0-a3
[prep-release-3.1.0-a3] Add migration for 3.1.0-a3
[prep-release-3.1.0-a3] Prepare Changelog
[prep-release-3.1.0-a3] Commit changelog for 3.1.0-a3
[prep-release-3.1.0-a3] Update version to 3.1.0-a4-dev for future development
Merge branch 'prep-release-3.1.0-a3' into develop