Bugfix langchain astradb metadata

[erichare]

This pull request fixes a bug in the Astra DB component which passes empty lists for the metadata include and exclude parameters, where the underlying langchain-astradb code explicitly expects them to be None (and providing empty lists for both results in an error).

        """
        Validate the constructor indexing parameters and normalize them
        into a ready-to-use dict for the 'options' when creating a collection.
        """
        params = [
            metadata_indexing_include,
            metadata_indexing_exclude,
            collection_indexing_policy,
        ]
        if params.count(None) < len(params) - 1:
            msg = (
                "At most one of the parameters `metadata_indexing_include`,"
                " `metadata_indexing_exclude` and `collection_indexing_policy`"
                " can be specified as non null."
            )
            raise ValueError(msg)