ICVP model changes

[litlfred]

• date should inculde a day, not just month and year or year (make it 10 characters as required)
• need required binding with administrrsative gender (it is based on the administrsative records of the source system)
• for nationality use iso 3166 for the country codes. required binding to refmart valueset https://worldhealthorganization.github.io/smart-refmart/CodeSystem-COUNTRYISO3.html
• ndt (document type) needs to be removed
• clarify issuer is "supervising clinician, or relevant authority responsible for issuing this certificate, or for overseeing the administering centre"
• The validity of this certificate shall extend until the date indicated for the particular vaccination or prophylaxis. This applies to the vaccine certificate, not any diigital certificates used for signing.

[litlfred]

@grahamegrieve