[FEATURE] Add support for BM25 indexing and retreival

[amanthegreatone]

Describe the feature you'd like
Add support for BM25 indexing and retrieval for the document store

Additional context
I was exploring how to improve RAG accuracy and came across this concept of contextual retrieval (https://www.anthropic.com/news/contextual-retrieval). This mentions BM25 and fusion of results from semantic and BM25 search and then reranking.

Another reference (https://medium.com/@kachari.bikram42/from-search-to-synthesis-enhancing-rag-with-bm25-and-reciprocal-rank-fusion-872d21dc4ca7)

[McNickSistoPro]

+1