Review and develop new design for VectorStore

[markpollack]

Current vectorstore interface is lacking in two important areas

• Does not support other types of search other than similarity search
• Does not support full api coverate for admin cases, e.g. delete, update operations

[maxhov]

In its current form it also assumes that the content is next to the embeddings. Does it make sense to separate these two out? One could keep the actual data on disk, while keeping the (embedding) vector in a different place (e.g. Postgres).