feat: add support for Vertex AI

[Vibgitcode27]

Fixes : #84 and #110

This adds support for Vertex AI authentication alongside the existing API key method.

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the application's authentication capabilities by integrating support for Google's Vertex AI. This change provides a more robust and flexible way to connect to AI services, particularly benefiting users who require Workload Identity Federation (WIF) for secure access. The update allows for easy switching between API key and Vertex AI authentication methods through simple environment variable configurations, ensuring adaptability for various deployment scenarios.

Highlights

• Vertex AI Integration: Added comprehensive support for authenticating with Vertex AI, allowing the application to leverage Google Cloud's managed machine learning platform.
• Flexible Authentication Mechanism: Implemented a dynamic authentication selection process, enabling users to switch between Vertex AI and the existing API key method via environment variables.
• Configuration Updates: Introduced new environment variables (REACT_APP_USE_VERTEX_AI, REACT_APP_GOOGLE_CLOUD_PROJECT, REACT_APP_GOOGLE_CLOUD_LOCATION) to configure Vertex AI settings.
• Type Definition Refinement: Updated the LiveClientOptions type in src/types.ts to remove the explicit apiKey requirement, accommodating the new Vertex AI authentication flow which does not directly use an API key.

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[gemini-code-assist]

Code Review

This pull request adds support for Vertex AI authentication as an alternative to the existing API key method. The changes are generally good, introducing a factory function to handle the different authentication configurations. However, I've found a logical error in how the Vertex AI mode is enabled, which would cause the opposite of the intended behavior. I've also included some suggestions to improve code safety and consistency regarding environment variable handling and to update a related code comment that has become outdated.