For users wanting to serve single page applications with in-app routing (such as vue, react-router, etc), we should provide a handler that will treat a specific subset of paths as root, always serving the root index.html with the javascript application.

Some background:

Stack Overflow Q&A: https://stackoverflow.com/questions/58432345/cloudflare-workers-spa-with-vuejs/58439234

Cloudflare Community post (same user): https://community.cloudflare.com/t/cloudflare-workers-spa-with-vuejs/122864

Docs issue: cloudflare/workers-docs#439