Emit an event in a redis stream on scan

[alexgarel]

What

• We want to store additional events about products (see Add an event file to log events per product #9756).
• We will store them in openfoodfacts-query but we need to emit them in a redis stream, as they happen.
• The redis stream must be a separate stream (not the same as product updates).

Code pointers

You can find some code pointers here. If some are missing, feel free to add them yourself in this file, or to ask them.

Part of