What default retriever do I need to specify in this definition?
rerank_query_engine = vector_query_engine.from_args(
similarity_top_k=10,
node_postprocessors=[postprocessor],
)

How do I add a node_postprocessor to a RetrieverQueryEngine?

I'm looking to create Settings.embed_model=bm25. How would I do that?

How do I use a bm25-based model for embeddings?