DOC: Improper id_key for MultiVectorRetriever in Multi-RAG cookbooks

[SMAntony]

URL

https://github.com/langchain-ai/langchain/blob/master/cookbook/Multi_modal_RAG.ipynb
https://github.com/langchain-ai/langchain/blob/master/cookbook/Multi_modal_RAG_google.ipynb

Checklist

• I added a very descriptive title to this issue.
• I included a link to the documentation page I am referring to (if applicable).

Issue with current documentation:

The id_key string in the first highlight should be id_key or when creating Document class (last id_key highlight in the image), the metadata should be doc_id.

Because of this conflict, anyone following the cookbook will be unable to get any output after querying MultiVectorRetriever.

Please fix or point me to the doc which I should change to fix this issue. I would very much like to contribute.

Idea or request for content:

No response