New svg files to cache, but without an explicit enough name

[monsieurtanuki]

Problem

With the latest AppNewsProvider, we get the following message:
AssetCacheHelper: please download https://raw.githubusercontent.com/openfoodfacts/smooth-app_assets/refs/heads/main/prod/tagline/android/assets/donation_campaign/fr.svg and put it in asset somewhere like [assets/cache/fr.svg, assets/cacheTintable/fr.svg]

Of course we may cache a file called fr.svg, but that would be dangerous if next time another file would bear the same name but from another folder.

Proposed solution

An alternate cache system that would accept cached filenames like donation_campaign__fr.svg

[monsieurtanuki]

Now those filenames are explicit.