Provide ability to specify a similarity score threshold when performing similarity search

[shashankram]

I can't seem to find a way to specify the score threshold when using the similarity_search() API provided by the vector store impl.
E.g., The Redis implementation exposes this as a distance_threshold argument.

[hsm207]

The integration uses weaviate's hybrid search to perform the search. At the moment, hybrid search does not have a score threshold argument. It is a feature that's being worked on (see this bounty)