I want to be able to use Calkit in CI and see changes to artifacts in PRs

[petebachant]

We could have a command at the end of a GitHub Actions workflow like:

calkit hub update-pr ${{ github.event.pull_request.number }}

Not sure what the best format would be. If we're talking about a LaTeX publication, we could create a LaTeX diff and upload the PDF. We could build a special page on calkit.io for comparing branch artifacts side-by-side and link to that. Might make sense under a "Changes" section.

See #451 (comment) for more motivation

It may be good to also automatically create/update the workflow with:

calkit update actions-workflow --update-pr

[petebachant]

Example using purely GitHub Actions in calkit/example-basic#7