Add the new UK packager code normalization

[teolemon]

What

• Per Edward
• "Hello since in the UK we've changed our traceability codes from UK to GB for example the code for butter was UK WQ108 EC and now it's changed to GB WQ108 how would we map the new ones?"
• Per @hangy
• "If it's now changed for everything, it could be useful to update the normalization code at

  openfoodfacts-server/lib/ProductOpener/PackagerCodes.pm

  Line 94 in 27eaa8d

  my $normalize_uk_ce_code = sub ($countrycode, $code) {

  , so that existing codes might be updated automatically"

Part of

• Packager codes (Tracker) #5508