Add new model presence validates

- Only validate :date_of_birth and :postal_code presence when the
  application has configured Remote Census and their alias fields
  has values.

app/models/verification/management/document.rb

@@ -5,6 +5,8 @@ class Verification::Management::Document
   attr_accessor :document_type, :document_number, :date_of_birth, :postal_code
 
   validates :document_type, :document_number, presence: true
+  validates :date_of_birth, presence: true, if: -> { Setting.force_presence_date_of_birth? }
+  validates :postal_code, presence: true, if: -> { Setting.force_presence_postal_code? }
 
   delegate :username, :email, to: :user, allow_nil: true