Upsert documents into the index.
The upsert functionality should utilize the ID field of the content object if it is provided. If the ID is not provided, the upsert method is free to generate an ID for the content.
When an ID is specified and the content already exists in the VectorStore,
the upsert method should update the content with the new data. If the content
does not exist, the upsert method should add the item to the VectorStore.
Sequence of documents to add to the VectorStore.
Additional keyword arguments.
