Fix Version/s: None
Due to recent changes to DockerHub, docker pulls are rate limited. Thus our GitHub workflows that heavily use images in Docker Hub (namely documents that use lsstsqre/lsst-texmf) should log in.
We've created an org level secret in the lsst, lsst-dm, and lsst-sqre GitHub organizations called DOCKERHUB_SQREREADONLY_TOKEN that is a token corresponding to our sqrereadonly DockerHub account.
The purpose of this ticket is to add the login step to the document templates in lsst/templates.
Announced as https://community.lsst.org/t/recommended-update-to-latex-document-builds-log-into-docker-hub-from-github-actions/4685?u=jsick
I also updated DMTN-049 a real-world demo of this change.