apiv1.IdentityMappingRequest should not require authentic_source_person_id

[fabienpe]

The identity element of the /identity/mapping API spec is based on the Model.Identity in which authentic_source_person_id is required. However the point of the API call is to get the authentic_source_person_id. The type of identity element in the apiv1.IdentityMappingRequest should therefore be different.

[masv3971]

authentic_source_person_id, family_name, given_name or date_of_birth is not required, that has been change as it seems. I would like to avoid multiple types that does pretty much the same thing since it's easy to miss.