Add a manually dispatched workflow for maintainers to sync a Docker
release branch to a selected release tag.
The sync-release-branch job checks out the release branch, computes
the list of unmerged tags up to the requested tag via
scripts/unmerged-tags, merges them in order via scripts/sync-branch
using git merge --no-ff (resolving conflicts by taking the tag's
content), then pushes the result to a temporary branch.
The push-release-branch job runs after manual approval via the
docker-releases environment. It verifies that neither the release
branch nor the temporary branch moved since the sync job ran before
force-advancing the release branch and deleting the temporary branch.
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>
Paweł Gronowski