community[patch]: Add namespace to allow indexing multiple tables within the same schema

[clemenspeters]

Issue:

We're working on a tenant based SaaS platform where we use separate tables for each tenant (to avoid infinitely growing tables).

The createHnswIndex function translates into a query like

CREATE INDEX IF NOT EXISTS vector_embedding_hnsw_idx
        ON tenant_123_index USING hnsw ((vector::vector(1536)) vector_cosine_ops)
        WITH (
            m=16,
            ef_construction=64
        );

where the index name is always vector_embedding_hnsw_idx.
Within the same schema in PostgreSQL, the index name must be unique across all tables.

This means it’s created for the first tenant, but not for anyone else since then the index with that static name already exists.

This PR allows to pass an optional namespace string to createHnswIndex which is used a prefixing the index name.

@PetersClemens

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[bracesproul]

lgtm, thanks for pushing this update

[bracesproul]

The format CI action is failing, could you run yarn format from inside libs/langchain-community and push up the changes? Thanks