Add support for gemini-embedding-001 model

[ishaheen10]

Please add this embedding model to the list of supported Gemini ones. This is the model Gemini considers stable and is deprecating the rest.

Model name to paste in: gemini-embedding-001

When I use it currently with ax-llm, I get a 404, so am calling it directly from Gemini's API.

https://developers.googleblog.com/en/gemini-embedding-available-gemini-api/

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.