feat(vertex-ai): function calling: convert markdown 'samples' to python

[Valeriy-Burlaka]

Description

Convert Markdown 'samples' for Function Calling Guides & API Reference pages:

• The entire "How to create a function calling application" section (a tutorial-style series of steps that together compile into a function-calling application)
• The "Example syntax" section for the API Reference page.

Checklist

• [x] I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• [x] Tests pass: nox -s py-3.9 && nox -s py-3.12
• [x] Lint pass: nox -s lint

[snippet-bot[bot]]

Here is the summary of changes.

You are about to add 9 region tags.

• generative_ai/function_calling/example_syntax.py:26, tag generativeaionvertexai_function_calling_example_syntax
• generative_ai/function_calling/function_calling_application.py:22, tag generativeaionvertexai_gemini_function_calling_app_setup
• generative_ai/function_calling/function_calling_application.py:46, tag generativeaionvertexai_gemini_function_calling_app_declare_1
• generative_ai/function_calling/function_calling_application.py:61, tag generativeaionvertexai_gemini_function_calling_app_declare_2
• generative_ai/function_calling/function_calling_application.py:90, tag generativeaionvertexai_gemini_function_calling_app_declare_3
• generative_ai/function_calling/function_calling_application.py:135, tag generativeaionvertexai_gemini_function_calling_app_prompt
• generative_ai/function_calling/function_calling_application.py:145, tag generativeaionvertexai_gemini_function_calling_app_submit
• generative_ai/function_calling/function_calling_application.py:169, tag generativeaionvertexai_gemini_function_calling_app_invoke
• generative_ai/function_calling/function_calling_application.py:184, tag generativeaionvertexai_gemini_function_calling_app_generate

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[msampathkumar]

Putting a hold on all Generative AI samples development.

Thank you for your work Valeriy-Burlaka !