Fix content type of JS during AWS S3 sync

[JL102]

Error when loading module scripts: Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/plain". Strict MIME type checking is enforced for module scripts per HTML spec.

By default aws s3 sync sets the content type of js files to text/plain. I fixed it manually by doing this sort of workaround by hand: https://stackoverflow.com/a/72594767/5121242 but I need to update the sync scripts to do this automatically, before I do any sort of future deployment.