Use document-type enum for document upload

[dvacca-onfido]

Use document-types enum for upload_document endpoint.

Add document type below to the enum:

  - home_office_letter
  - birth_certificate
  - vehicle_registration_certificate
  - form_for_affixing_the_visa
  - identification_number_document

NB: this change will create breaking change in most of the libraries, a major update will be necessary.