Pin model version of gemini-pro for reproducibility

[koverholt]

Currently, this app points to the latest version of gemini-pro, which is an alias to gemini-1.0-pro.

Could you try with gemini-1.5-pro-preview-0409 and see if the app works as expected? If not, you can pin to version gemini-1.0-pro-001 instead as a stable model checkpoint. You should be able to swap model versions without updating the SDK code.

Also note that google-cloud-aiplatform 1.48.0 is the latest Python SDK version: https://pypi.org/project/google-cloud-aiplatform/