Getter for the gRPC stub used for the Table Admin API.

        For example:

        .. literalinclude:: snippets.py
            :start-after: [START bigtable_instance_admin_client]
            :end-before: [END bigtable_instance_admin_client]

        :rtype: :class:`.bigtable_admin_pb2.BigtableInstanceAdmin`
        :returns: A BigtableInstanceAdmin instance.
        :raises: :class:`ValueError <exceptions.ValueError>` if the current
                 client is not an admin client or if it has not been
                 :meth:`start`-ed.

def instance_admin_client(self):
        """Getter for the gRPC stub used for the Table Admin API.

        For example:

        .. literalinclude:: snippets.py
            :start-after: [START bigtable_instance_admin_client]
            :end-before: [END bigtable_instance_admin_client]

        :rtype: :class:`.bigtable_admin_pb2.BigtableInstanceAdmin`
        :returns: A BigtableInstanceAdmin instance.
        :raises: :class:`ValueError <exceptions.ValueError>` if the current
                 client is not an admin client or if it has not been
                 :meth:`start`-ed.
        """
        if self._instance_admin_client is None:
            if not self._admin:
                raise ValueError("Client is not an admin client.")
            self._instance_admin_client = _create_gapic_client(
                bigtable_admin_v2.BigtableInstanceAdminClient
            )(self)
        return self._instance_admin_client