Add filebrowser image

[rgaudin]

For Nomad, Math Mathews, Africatik and more to come (according to @Popolechien), we need a generic app that serves static files with or without an index page.

This would be nicely done using a caddy image configured with file_server.

In an initial version, as all packages have a support webpage, that would be enough.

Later, we could invest some time to tweak the template so it's better integrated and/or more practical.

[kelson42]

Might be possible to make the ZIM files available for download via this?

[rgaudin]

Absolutely ; that's a great idea.