Creates a new contact and returns the full contact representation.
Creating an office (organisational unit): To create an office, set the parent_id field to the ID of the parent contact. Offices inherit tin_value and tin_scheme from the parent contact; if provided, these must match the parent's values exactly, otherwise the request is rejected with 422 Unprocessable Entity.
Independent CIN for offices: Unlike tin_value, cin_value and cin_scheme are stored independently on the office. If not provided, the office inherits cin_value from the parent contact.