Deploy to npm tag from branch

[cwillisf]

Proposed Changes

Main change: allow the "Publish" workflow to publish to a tag other than latest, depending on the branch name and the state of the "Prerelease" checkbox in GitHub's release UI.

Additional changes:

• commitlint now runs as a separate workflow instead of as part of the CI workflow, so you can tell the difference between a commitlint failure vs. a build/test failure.
• the release commit message now follows Conventional Commit style.

Reason for Changes

This allows the spork branch to publish to the spork tag on npm, making it easier to test on staging. Other branches are likely to want this soon, so I pulled this out of the spork branch so we don't need to wait for all the spork QA to finish before those other branches can use this change.

Test Coverage

I've already used this workflow from the spork branch.

[cwillisf]

Closing in favor of #222