Use parameters countries= when fetching insights

[raphael0202]

Country filtering does not work any longer (ex: https://hunger.openfoodfacts.org/questions?type=label&country=en%3Afrance), because country= parameter is not working any longer for the following endpoints:

• /questions/random
• /questions/popular
• /questions/unanswered
• /questions
• /insights/random
• /insights
  The countries parameter should be used instead with a two-letter code (it accepts several countries).
  I thought I had created an issue on Hunger Games, but I obviously didn't, sorry for that!

And by the way, /questions/random and /questions/popular are deprecated in favor of /questions?order_by={random,popularity}:
https://openfoodfacts.github.io/robotoff/references/api/#tag/Questions/paths/~1questions/get