Add FoodEx2 links to the taxonomies

[teolemon]

Problem

• The French DGCCRF told us they had invested into FoodEx2 compatibility on one of their tools
• I'm unsure how much FoodEx2 is used, but it might be worth adding links to this European standard
• Wikidata already has a FoodEx2 property, and we already have Wikidata links, so we could start by fetching those
  • Code FoodEx2 (rev2) (P4637) - identifier within the FoodEx2 (version 2 of the EFSA Food classification and description system for exposure assessment) food taxonomy anglais
• An old wiki page also shows their comprehensiveness on raw food: https://wiki.openfoodfacts.org/Global_categories_taxonomy/Foodex2

Part of

• External ontologies
• Taxonomies