fix: Pass along model version in GenerateContentResponse

[Annhiluc]

Description of the change

Pass along model version in GenerateContentResponse.

• Ran python docs/build_docs.py to update documentation.
• Ran pytest with no failures.

Motivation

b/378140421

Type of change

Bug fix

Checklist

• [x] I have performed a self-review of my code.
• [x] I have added detailed comments to my code where applicable.
• [x] I have verified that my change does not break existing code.
• [x] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• [x] I am familiar with the Google Style Guide for the language I have coded in.
• [x] I have read through the Contributing Guide and signed the Contributor License Agreement.

[Annhiluc]

Thanks Mark for the review! Reverted docs.

Tests are failing because the generated client library doesn't have that attribute.

To clarify, did I miss adding the model_version somewhere or has the client library already added this attribute and it hasn't been released yet? How can I check on the release of the client lib?

[MarkDaoust]

I need to release a new version and update the dependancies in setup.py.

cl/693090666