Store number of unique scans by country for the last year in the product object

[stephanegigandet]

We currently have one popularity sort key that is the same for the whole world. So the order of products by popularity is the same in all countries (but some are filtered if they are not sold in the country).

We currently store scans statistics in a JSON file next to the product .sto files:

• Improve scanbot, generate more accurate country top products, store each product scans in scans.json files #5083

In order to be able to show popular products by country, we could store the raw number of scans for each country in the last year directly in the product object.

e.g. unique_scans : { world : 1000, fr : 750, be: 200, nl: ... } etc.

• This would also allow to show those numbers to users Indicate the number of scans #8668

• and to producers Show the number of scans to food manufacturers in the Pro platform  #9741

We could also remove the popularity key (which is a bit complex as it uses unique scans, top scans, and date of last image), if we can find a way to get sorted products by unique_scans in a country (primary key) and by another field like last_modified_t (secondary key) so that we have a unique ordering of products (in order to have products by page).

This unique_scans by country could be saved in off-query, so that we can sort on it to retrieve lists of products.