docs: def xgroup_create(self, name, groupname, id='$', mkstream=False):
          """
          Create a new consumer group associated with a stream.
          name: name of the stream.
          groupname: name of the consumer group.
          id: ID of the last item in the stream to consider already delivered.
          """
          pieces = ['XGROUP CREATE', name, groupname, id]
          if mkstream:
              pieces.append(Token.get_token('MKSTREAM'))
          return self.execute_command(*pieces)