Configure Astro prefetch behaviour

[jbmoelker]

User stories

As a website visitor,
I want web pages to be prefetched,
so that navigation is instant when I hit a link.

As a website editor,
I want web pages to be cached only shortly,
so that the changes I make propagate reasonably quickly.

Approach

Use Astro's prefetch feature.

Questions

• Which default strategy should we use (hover, tap, viewport, load)?
• Do we add caching headers for better Firefox and Safari support? Cloudflare doesn't provide ETags, but we could add short Cache-Control and Expires headers either through public/_headers config or in a Service Worker (see Add Service Worker #199). Through a Service Worker we could even add our own ETags 🤔.
• If our default prefetching is conservative (hover or tap), should we add inline hints [data-astro-prefetch="load"] to the main menu items (see Editable site menu #196)?