Track missing postinstall script execution on Netlify

[sebastinez]

This issue is to track the missing postinstall execution, that we see in our Netlify builds.

While npm install and the subsequent npm run build are being triggered we don't see the postinstall scripts running, which means we don't get the twemoji and katex assets in our builds. While a manual cache clearing removes the issue, this should be something we can automate.

Here are some PRs and issues that are seeing the same issue with Netlify on the build-image repo. https://github.com/netlify/build-image/issues/113 https://github.com/netlify/build-image/issues/523