Gemma chat notebook update: add Gemma 2 model info

Description of the change

Launch of Gemma 2 models

Choose one: Documentation

[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.