feat(gemini): add notebooks on google-adk session and memory

[msampathkumar]

• notebook: session
• notebook2: memory

Description

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• [ ] Follow the CONTRIBUTING Guide.
• [ ] You are listed as the author in your notebook or README file.
• [ ] Your account is listed in CODEOWNERS for the file(s).
• [ ] Ensure the tests and linter pass (Run nox -s format from the repository root to format).

Fixes #<issue_number_goes_here> 🦕

[holtskinner]

@msampathkumar I actually wonder if it would make more sense to put this in the ADK Samples repo. https://github.com/google/adk-samples