Automate Java SDK releases - #3127

I did a AI assisted review and found a few issues

For a pull request, the workflow passes the current target branch SHA as BASE_SHA and the feature branch SHA as HEAD_SHA. The candidate script requires BASE_SHA to be an ancestor of HEAD_SHA. Once main advances after a feature branch is created, that condition is false even for a valid, mergeable PR. This also rejects ordinary PRs that only add notes under [Unreleased]. I reproduced this with a small Git repository: branch feature, advance main, add a changelog entry on feature, and run release.sh candidate with the two branch heads. It exits 1 with The base commit must be an ancestor of the release commit. The new test fixture uses a linear history and misses this case. I think this would impact us if we needed to do a patch release of old versions. The setup instructions say to restrict that environment to main but we should also be able to release from other branches for back-porting fixes .

I think this would impact us if we needed to do a patch release of old versions. The setup instructions say to restrict that environment to main but we should also be able to release from other branches for back-porting fixes .

I checked the last time we did a branch release and it was quite a while ago, so I wasn't sure if we should support that out of the box. I can make sure it is supported though.