Gradle maintenance

[scordio]

We've been falling behind with the Gradle-related maintenance in this project.

So far, I see the following tasks requiring attention:

• [ ] Adopt gradle/actions/setup-gradle and remove gradle/wrapper-validation-action
• [ ] Add a new dependency-submission workflow
• [ ] Check setup for org.ajoberstar.git-publish and org.asciidoctor.jvm.convert, and upgrade to the latest versions