add release.yaml to automate release notes generation

[akirafujiu]

Summary

Here is another automation flow to create release note based on https://docs.github.com/en/repositories/releasing-projects-on-github/automatically-generated-release-notes. It should consume labels on issues & prs, then group them into sections in a release note.

Here is a result which I tested on my forked repo: https://github.com/akirafujiu/etcd-java/releases/tag/0.0.1-test

[akirafujiu]

@njhill Could you please review this as well? It has no impact on actual codes itself