Replace circle-ci deployment with GitHub Actions

[AlexLakatos]

Circle CI is running out of memory, and failing to deploy the builds.

We should take this opportunity to swap deployments to GitHub actions.

The current setup uses the yarn deploy command (build the website, and commit it to the gh-pages branch, which takes care of the hosting). I think we should be able to replicate that for GitHub Actions.

[huijing]

Notes

Netlify build took around 2min 14s.

Test deploy GH action ran successfully in 208s.