[Bug]: Prompt Optmizer using invalid model

### File Name

https://github.com/GoogleCloudPlatform/generative-ai/blob/main/gemini/prompts/prompt_optimizer/vertex_ai_prompt_optimizer_ui.ipynb

### What happened?

Looks like somewhere in the code is trying to use gemini 1.5 pro and referencing it through an invalid url.

### Relevant log output

```shell
Detailed error: Error: The job failed: 404 Publisher Model `projects/XXXXX/locations/us-central1/publishers/google/models/gemini-1.5-pro-002` was not found or your project does not have access to it.
```

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