Product Manager for GitHub Actions here. Sorry that this was difficult for you - we're continuing to work on our documentation for both GitHub Actions and Github Packages (and how to use them together) and we'll make sure that we improve this.

For my Java project, I set up GitHub Packages as a server in my settings.xml, and then use:

mvn deploy -Dgithub.username=${{github.actor}} -Dgithub.password=${{github.token}} -s settings.xml

as a step in my GitHub Actions workflow.

I'm not super familiar with maven, so I'll talk with the Packages team about how we can improve the documentation here.