Use github pages instead of vercel

[jkleiber]

Summary
We aren't leveraging vercel's hosting service other than for serving a static site. This could also be done on Github Pages, and could be better for our roadmap (Vercel starts charging money for multiple users managing the site, while Github Pages is manageable by everyone with appropriate permissions in this organization).

The objective of this ticket is to stand up a Github Pages deployment workflow, as well as a PR preview workflow. Once this is done, we can migrate away from Vercel.

Work Scope

• Determine how to package the app to correctly for Github Pages
• Create a Github Pages deploy workflow for continuous deployment
• Create a Github Pages preview workflow for PR reviews