[gatsby] Add `@vercel/gatsby` Builder

[lydiahallie]

This PR adds support for the following Gatsby 4, including SSR, DSG and API routes.

⚠️ Note: Redirects have to be added manually in the Vercel config file.

[EndangeredMassa]

The yarn.lock file appeared to have dupe entries for ncc. Maybe this was the result of a merge? It was causing this error:

ERROR  yarn.lock: could not unmarshal lockfile: yaml: unmarshal errors:
  line 3222: mapping key "@vercel/[email protected]" already defined at line 3191

I pulled this down, ran yarn install, and the updated yarn.lock appears to be OK. I pushed that commit up. If something else was wrong, I can revert this change.

[TooTallNate]

The tests are now passing here, but I think it's a false positive because vc build isn't actually using this Builder yet since it's not listed in the framework's useRuntime prop.

[TooTallNate]

It looks like we still need prepareCache() implemented in this Builder as well. The current configuration (when going through @vercel/static-build) is {.cache,public}/**.

[leerob]

Thanks for all your help here! I know this is a large, gnarly addition 😄

[rwitchell]

hi @lydiahallie - how can I test this on my build? Any idea when this will be merged?

[vercel[bot]]

Deployment failed with the following error:

Creating the Deployment Timed Out.

[Ethan-Arrowood]

closing in favor of @vercel/gatsby-plugin-vercel-builder