Check ZIM file status before redirecting

[audiodude]

Inspired by #819

ZIM files on Wasabi storage expire after 2 weeks. In WP1, we measure if it has been 2 weeks since the ZIM was requested and attempt to show a message that "Your ZIM has expired (2 weeks). Please re-request". However this message can be easy to miss.

It would be nice if we pre-fetched the wasabi URL with requests, perhaps only a HEAD request. If the status comes back as 404, we can redirect to frontend page that explains that the ZIM has expired and provides a button for re-requesting it.

[kelson42]

Indeed, that would be IMHO a lot more robust.