[DRAFT] Feature - add in memory vector store

[jaigouk]

changes

• added in memory based similarity vector store
• changed argument for EmbedViaOpenAI from openai_connection to client

why

• we need to provide more options for embedding methods
• relying on openai embedding only may lead to too many API calls
• resolves part of https://github.com/BoxcarsAI/boxcars/issues/60

[jaigouk]

I think we need to clean up the hnswlib also. I will try to do that with another PR.