Allow user to download xls/csv of the opportunities for improvement

[manon-corneille]

Fields to export :

• EAN
• Category of improvement (Category comparison VS Nutri-Score)
• Type of improvement (eg. "Better Nutri-Score with much less energy" or "High sugar content for this category")
• Value for the product (only applies for product with category comparison improvement)
• Mean value of the category (only applies for product with category comparison improvement)
• Value nutrient current (only applies for product with Nutri-Score improvement)
• Value nutrient targetted (only applies for product with Nutri-Score improvement)
• Difference in percent (only applies for product with Nutri-Score improvement)

This would make it easier for R&D teams to manipulate the data, and hopefully would encourage them to take action on reformulation.
We could also imagine sending this export automatically once or twice a year to producers.

[teolemon]

Probably a duplicate of #10564