[Feat]: Add more interactivity to Streamlit & Vertex AI sample

[telpirion]

Is your feature request related to a problem? Please describe.

Reading through the Cloud Run application utilizing Streamlit Framework that demonstrates working with Vertex AI Gemini API, it seemed like the lesson didn't provide as many opportunities for learning as I would have liked.

Describe the solution you'd like

I would revise the sample to be more interactive: pose more choices to the reader, provide more description of what is in the app.py file, explain where & how the Vertex API is integrated into the sample.

Describe alternatives you've considered

No response

Additional context

No response

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