Integrate KiwixStorage #223
Description
Ours scrapers all depend on S3 and use KiwixStorage for it. That wrapper and repo are mostly untouched (yet working) and would great benefit from being integrated into scraperlib: tests, usage, dependencies update, better API, etc.
Now that we had experience using it, it probably make sense to reduce its API to what's actually used.
It's true that some non-scraper projects are using it (cardshop and zimfarm to upload to S3), but those are also using scraperlib and we've discussed making scraperlib's dependencies more modular via extras anyway.