Add i18n for VAT number quote validation item
Add i18n for VAT number quote validation item

The key for this field was missing from the i18n items. Was previously
just returning the key rather than a useful error message.

uktrade/data-hub-frontend,uktrade/data-hub-fe-beta2,uktrade/data-hub-frontend,uktrade/data-hub-fe-beta2,uktrade/data-hub-frontend