Git submodules config

[joshuata]

This migrates the toolkit builder to git submodules from the previous github actions-based setup. This has several beneficial properties:

• The build environment is now fully contained within the repo. Previously a developer would need to checkout each repo individually in order to mimic the actions of the build bot. Now both can simply clone/pull the repo and have everything automatically setup
• The build state is reproducible. If two users checkout the same commit and build the site, they will get identical outputs.
• The repository is more resilient to problems with the dependent components. If one of the components ends up with a bug in their main branch that causes the build to fail, it can be caught in the pull request attempting to update the submodule rather than during deployment.
• Because the build state is fixed, you only need to deploy when a change is merged or pushed to main. This helps maintain the cloudfront cache and reduces compute usage