Releasing rules_platform

1. Update version in distro/BUILD.bazel,
2. Build the release running bazel build //distro:rules_platform-{version}
3. Prepare release notes running bazel build //distro:relnotes
4. Create a new release on GitHub
5. Copy/paste the produced relnotes.txt into the notes. Adjust as needed.
6. Upload the produced tar.gz file as an artifact.