Allow same id for different collections

[mayrop]

It would be nice to have the ability to have the same ID for different collections. This would be useful for situations where, let's say I want to create embeddings for a table called books for 2 columns "short_title" and "title", referencing different collections but same ID (same book).

Current behavior is that even though the diff collection is added to the vectorstore, if the same id is provided, it will overwrite the entire row.

Primary key then would be the combination of id + collection_id.