Add winery backend: learning the codebase

This is my first time contributing to the Software Heritage codebase. I've studied it a little and I'm pretty sure it won't be too difficult to figure out what's where and how things should be done. But it will take me a few days to get comfortable.

• Study the object storage module in detail
• Search for a trivial bug or improvement to implement
• Kindly ask if someone is willing to review the patch that will be submitted to the object storage module

Outcome: a merged patch to the object storage module

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Migrated from T3522 (view on Phabricator)