Automated PDF build as artifacts

[jakebeal]

Per #8, we definitely want draft PDFs readily accessible to folks who aren't wanting to build the LaTeX.

I think we don't want to accumulate lots of PDF diffs in the git, so we probably should do something like the automated LaTeX build that SBOL visual uses.

SBOL visual's workflow: https://github.com/SynBioDex/SBOL-visual/blob/master/.github/workflows/main.yml