ci: Workflow to check PR for conventional commit format

[chipkent]

• PRs will need to adhere to the conventional commit specification: https://www.conventionalcommits.org/en/v1.0.0/
• If they do not, a comment will be added to the PR with details about the spec
• Goal is to automate prettier release notes (e.g. separate Features from Fixes, highlight Breaking Changes). Could potentially be used for automated version bumping as well (which we do in deephaven-plugins, automatically bumping the correct version based on if there are breaking changes (major), features (minor), or fixes only (patch) in the release.
• Follow up:
  • Add this check to branch protection
  • Use the commit history to automatically generate the changelog. In the deephaven-plugins repo, we use cocogitto, which also automatically bumps the version
  • Recommend to use PR_BODY and PR_TITLE for the default squash_merge_commit_mesage and squash_merge_commit_title

I also noticed that with GitHub's automated release notes, you can actually configure it to use the labels to categorize PRs. That could be useful if there's hesitation to using conventional commits. One advantage of conventional commits is that you can easily handle automatic version bumping (we use cocogitto), which I don't think GitHub can do.

See deephaven/deephaven-core#5528