docs(genai): Update quickstart_example.py to use us-east4 as default region

[holtskinner]

Description

• us-central1 became allowlist only for new projects

[gemini-code-assist]

Summary of Changes

Hello @holtskinner, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the quickstart_example.py file to use us-east4 as the default region for Vertex AI initialization. This modification addresses an issue where us-central1 is no longer available by default for new projects, ensuring that users can successfully run the quickstart example without encountering region-related access restrictions.

Highlights

• Default Region Update: The default Vertex AI initialization region in quickstart_example.py has been updated from us-central1 to us-east4.
• Reason for Change: This change was necessary because us-central1 is now allowlist-only for new projects, which could prevent users from running the quickstart example.

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[gemini-code-assist]

Code Review

This pull request correctly updates the region from us-central1 to us-east4 in the quickstart example, addressing the new access restrictions on us-central1. However, the change appears to be incomplete as several other files in the generative_ai/rag/ directory still use the us-central1 region. To ensure all examples and tests function correctly for all users, I recommend extending this change to all relevant files. The files that still reference us-central1 include:

• generative_ai/rag/test_rag_examples.py
• generative_ai/rag/create_corpus_example.py
• generative_ai/rag/generate_content_example.py
• generative_ai/rag/retrieval_query_example.py

Updating these files as part of this PR will ensure consistency across the codebase.

[gemini-code-assist]

To improve maintainability and consistency with other files in this directory (like test_rag_examples.py), consider defining the location as a module-level constant (e.g., LOCATION = "us-east4") at the top of the file and using that constant here. This makes it easier to update the region in the future if needed.