Add support for the Knowledge Panels for Facets API

[teolemon]

What

• A new API that emulates knowledge panels but for facets (eg /category/wines) has been created, and deployed to pre-prod
• Theoretically, the API should work exactly like the knowledge panels displayed on a product (same format)
• Only the endpoint changes. But that's theory at this point.
• https://facets-kp.openfoodfacts.net/docs#/knowledge-panel/knowledge_panel_knowledge_panel_get
• This unlocks value when implemented within Introduce a way to explore all Open Food Facts facets (a taxonomy explorer) smooth-app#2737

Part of

• 🎯 What can I work on ? (Dart SDK) #218

[sumit-158]

Eg:- for category-fr: fitou
https://facets-kp.openfoodfacts.net/knowledge_panel?facet_tag=category&value_tag=fr%3Afitou

[teolemon]

Now deployed to production: https://facets-kp.openfoodfacts.org/knowledge_panel?facet_tag=category&value_tag=fr%3Afitou