Obsolete dates should be ISO-8601

[CharlesNepote]

Currently, dates related to obsolete products are stored as is:

    "obsolete_since_date": "2023/07/01",
    "obsolete_since_date_imported": "2023/07/01"

(Example.)

Since a very long time in Open Food Facts we use ISO-8601 international date format, which tends to be a common international standard in many fields (data science, research, economy, etc.). The dates should be written: 2023-07-01.

Part of

• ⬇️ Data exports (tracker) #6429
• 🗄 Obsolete products (tracker) #8814

[github-actions]

This issue has been open 90 days with no activity. Can you give it a little love by linking it to a parent issue, adding relevant labels and projets, creating a mockup if applicable, adding code pointers from https://github.com/openfoodfacts/openfoodfacts-server/blob/main/.github/labeler.yml, giving it a priority, editing the original issue to have a more comprehensive description… Thank you very much for your contribution to 🍊 Open Food Facts