wrong tutorial

[NavodPeiris]

Description of the bug:

https://github.com/google-gemini/cookbook/blob/main/examples/Talk_to_documents_with_embeddings.ipynb

embeddings usage here is wrong.

but for both query and document, the same RETRIEVAL_DOCUMENT type embedding was used. also it should be "RETRIEVAL_DOCUMENT" not "retrieval_document"

[Surjasa]

I fixed the incorrect embedding usage & casing described here and opened a PR #1032