Build: Create GitHub Action for Building Firebase

[ovflowd]

This issue concerns an Infrastructure enhancement to use GitHub Actions to build the Production builds and deploy to Firebase instead of G Cloud.

To also speed up Gatsby builds (whose are being held back due to cache issues), we want to take advantage of Gatsby's incremental build system and use (https://github.com/marketplace/actions/cache) to keep the cache of Gatsby's build .cache and (https://github.com/actions/setup-node) (https://github.com/actions/setup-node#caching-global-packages-data) to cache NPM packages.

This should increase the speed of our builds from ~6 minutes (GitHub Action) to around ~1 minute or less.

I also found an example config (outdated) similar to what we would do: https://github.com/codewithkristian/gatsby-incremental-builds-gh-actions-example/blob/master/.github/workflows/build.yml

[bnb]

FWIW worth noting that if this does get moved to nodejs.org, we will almost certainly not want to run on Firebase (or GCloud) since we have existing infra.