Fix NINO validation for GB

[strotgen]

The prefixes in the code are based on documentation archived in 2012. This PR updates the validation rules to use the most recent and accurate ones.

New validations: https://www.gov.uk/hmrc-internal-manuals/national-insurance-manual/nim39110

All prefixes are valid except:

• The characters D, F, I, Q, U, and V are not used as either the first or second letter of a NINO prefix.
• The letter O is not used as the second letter of a prefix.
• Prefixes BG, GB, KN, NK, NT, TN and ZZ are not to be used