code: def member_add(self, repl_id, params):
          
          repl = self[repl_id]
          member_id = repl.repl_member_add(params)
          self[repl_id] = repl
          return member_id
docs: create instance and add it to existing replcia
          Args:
              repl_id - replica set identity
              params - member params
  
          return True if operation success otherwise False