file_server fallback to index.html

[kyeotic]

Is your feature request related to a problem? Please describe.

Using statically-generated single page applications, such as those produced by Vite, return 404 for dynamic deep links, since those paths are not backed by real files.

Describe the solution you'd like

An option to fallback to S{fsRoot}/index.html} for missing paths.

Describe alternatives you've considered

• Use hash routes. Sub-optimal because it impacts user-facing routes
• Use oak. Sub-optimal for Deno Deploy when compared to

cd dist/ && deployctl deploy --prod --project=$PROJECT_NAME https://deno.land/std@0.171.0/http/file_server.ts

• This stupid wrapper (I just made this)