Use GitHub Packages directly in action.yml files

[s0]

Docker images published to http://docker.pkg.github.com/ can't directly be used in action.yml files via docker://, for a couple of reasons:

• the docker package registry currently requires HTTP auth, including for public repositories
• the actions docker daemon doesn't authenticate with docker.pkg.github.com by default

Workaround

To work around this, course templates need to currently specify their own action locally, that builds a Dockerfile locally that references the course image, and the workflow files need to add an additional step to authenticate with docker before running the course action.

Once Fixed

Once this is no longer the case, and actions.yml files can directly reference docker images on docker.pkg.github.com, the following changes need to be made in this repository:

• The action .github.to.move/workflows/action/ directory should be deleted
  from templates/learninglab/course-template
• The workflow file templates/learninglab/course-template/.github.to.move/workflows/check-queries.yml should be updated to address the TODO comments
• Instructions should be updated in templates/learninglab/README.md to instruct course creators to modify the uses property in .github.to.move/workflows/check-queries.yml instead of updating the Dockerfile.

[xcorail]

cc @adityasharad

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