[feat] `vector_strategies` for vector db indexing

[pkarw]

It would be really cool to add indexing strategies for this data later on. Right now we have storage_strategies, which is fine, but I'm thinking of something like vector_strategies with pineconedb, pg_vector, and similar approaches—so that PDF documents are stored directly in a vector database. How awesome would that be? Then you could immediately set up a RAG (Retrieval-Augmented Generation) workflow!