Actions: create workflow to tag/publish a version #13

Go packages are basically tags in GitHub, so we need workflows that handle preparing and publishing bugfix and release versions. Bugfix versions are based on a previous release version, and contain only the fix (or fixes), but no new features.

release.yaml

• take release version as input, fail if patch version is not 0
• create + push tag on main
• create GH Release

prepare_bugfix.yaml

• checkout tag, read version X.Y.Z
• compute patch version N = Z+1, create branch named bugfix/X.Y.N
• push new branch

publish_bugfix.yaml

• take branch as input, fail if main is selected
• run build + tests
• create + push tag on branch
• create GH Release

Note: updating pkg.go.dev manually is not needed, that happens automatically