Deliver proper ZIM "favicon" for screens with dpr > 1

[kelson42]

More and more screens have a (device pixel ratio) > 1. Unfortunately on these screens, our current favicon delivered by ZIM Metadta `Illustration_48x48@1" does not deliver enough information to be displayed properly.

Based on the dpr value delivered by the Web browser, kiwix-serve should use Illustration_48x48@1", Illustration_48x48@4" or `Illustration_48x48@3" (this list is not exhaustive).

Blocked by openzim/libzim#937

[kelson42]

@rgaudin agree how this should work?

[rgaudin]

@rgaudin agree how this should work?

I think we should simply list all available illustration variants with their respective DPR for the browser to decide ; yes.

I dont understand what this is doing in kiwix-tools though as this is libkiwix.