feat: sentiment analysis sample for Vertex LLMs

[gericdong]

Description

Fixes b/281562687

Add a sentiment analysis sample for Vertex LLMs.

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• ai-platform/snippets/predict-text-sentiment.js:20, tag aiplatform_sdk_sentiment_analysis

---

This comment is generated by snippet-bot.
If you find problems with this result, please file an issue at:
https://github.com/googleapis/repo-automation-bots/issues.
To update this comment, add snippet-bot:force-run label or use the checkbox below:

• Refresh this comment

[telpirion]

I would consider cutting this paragraph and the next since it references actors by name.

[gericdong]

Agreed. Removed content.

[telpirion]

It looks like this is missing a sentiment value.

[gericdong]

I see. The sentiment is supposed to be missing here. This is the prompt for the model to predict.

[gericdong]

/gcbrun