[Feat]: Can we add more examples of agents that support vertex ai access?

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

It seems that only google_adk in the current samples/agents supports vertex ai access. Can we provide more agents that support vertex ai access? Thanks ~

### Describe the solution you'd like

Hope to introduce more vertex ai access agents instead of GOOGLE_API_KEY

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Examine the existing `google_adk` agent in the samples/agents directory to understand the Vertex AI access pattern. Look for other agent implementations that could be adapted to use Vertex AI instead of a GOOGLE_API_KEY. The goal is to create new sample agents that demonstrate this integration. Check the project's README or contributing guidelines for how to add new samples.

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