feat: Add/update “whole grain” ‘nutrient’ categories

[Freso]

Amount of “whole grain” content in a product is fairly common to state on e.g. breads in Denmark and Sweden at least, often given as something like “amount of whole grain in the product is X [% or g] which corresponds to Y% of the dry weight.”

Swedish example text (I wasn’t able to find anything prescribing this specific formulation though, but see Swedish example products.):

Fullkornshalten i brödet är X% vilket motsvarer Y% av torrvikten

The Danish Whole Grain Partnership require products marked with the Whole Grain logo to state (p. 13 of “Fuldkornsmanualen”/p. 12 of the “Whole Grain Manual”):

Fødevarestyrelsen anbefaler 90 gram fuldkorn om dagen og gerne mere
som en del af en varieret kost. Produktet indeholder X gram fuldkorn
pr. 100 gram[, når det tilberedes efter vejledningen på pakken].

Example products:
https://se.openfoodfacts.org/product/7311070008494/lantgoda-surdegsbr%C3%B6d-p%C3%A5gen
https://se.openfoodfacts.org/product/7311070008432/r%C3%A5glevain-p%C3%A5gen
https://se.openfoodfacts.org/product/7311070008609/k%C3%A4rnsund-surdegsbr%C3%B6d-p%C3%A5gen
https://dk.openfoodfacts.org/product/5701246036727/rug-sandwich-kohberg
https://dk.openfoodfacts.org/product/5701246106727/rugbr%C3%B8ds-boller-kohberg

Slack discussion:
https://openfoodfacts.slack.com/archives/C06A7LENM/p1751699819264629

Sources:
https://kontrollwiki.livsmedelsverket.se/artikel/398/nyckelhalet-ord-och-definitioner#fullkorn
https://fuldkorn.dk/om-partnerskabet/fuldkornslogoet/
https://fuldkorn.dk/en/about-us/the-whole-grain-logo/
https://wholegrainscouncil.org/whole-grains-101/how-much-enough/whole-grain-guidelines-worldwide

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.74%. Comparing base (8aee300) to head (3ee99ce).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12129   +/-   ##
=======================================
  Coverage   50.73%   50.74%           
=======================================
  Files          90       90           
  Lines       24055    24055           
  Branches     5781     5781           
=======================================
+ Hits        12205    12207    +2     
  Misses      10348    10348           
+ Partials     1502     1500    -2     

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