JOSS Build Action

[kylegodbey]

We should add a github action to automatically build the paper:

https://joss.readthedocs.io/en/latest/paper.html#checking-that-your-paper-compiles

https://github.com/marketplace/actions/open-journals-pdf-generator

[dashertr]

I've implemented this such that a zip file containing the pdf is created in the actions artifacts. Currently, the PDF is not committed to the repo, but we could add a step to do that.