Co-authored-by: Marcus Schiesser <mail@marcusschiesser.de>

Co-authored-by: Yi Ding <yi.s.ding@gmail.com>

Co-authored-by: Alex Yang <himself65@outlook.com>

Allows our scripts to be run repeatedly with vector store backing and
persistence without throwing an error.

This is rudimentary support which doesn't work if the document has
changed over time.

Also added the insert and delete functions so that documents can be
added manually.