code: def addAttribute(self, attrib: Attribute):
          
          self._attributes[attrib.key()] = attrib
          req = attrib.ledgerRequest()
          if req:
              self.pendRequest(req, attrib.key())
          return len(self._pending)
docs: Used to create a new attribute on Sovrin
          :param attrib: attribute to add
          :return: number of pending txns