fix: Nutri-Score v2 fixes and improvements to knowledge panels

[stephanegigandet]

• use "undef" in the nutridscore data instead of 0 for fiber, fruits/vegetables/legumes values etc. when they are not known
• in the Nutri-Score panel, display "unknown" instead of 0 when a nutrient is unknown
• count the number of non-nutritive sweeteners (for beverages) and display it, instead of just indicating absence / presence
• fixes some warnings including Warnings when computing Nutri-Score #9781
• add some missing strings in en.po
• some bug fixes for special cases (like spring water with no nutrition data, where we do display Nutri-Score A anyway)

[teolemon]

• Can we put the "Nutri-Score not applicable" explanations at the top of the hierarchy (and not in details of the computation) ? (example: https://world.openfoodfacts.org/product/4009900484695/wrigley-s-orbit). The sweet extra mile would be a small explanation of why they're actually excluded.
  

[alexgarel]

Good !

[sonarcloud]

Quality Gate passed

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