feat: text classification sample for Vertex LLMs

[gericdong]

Description

Fixes b/281562687

Add a text classification sample for Vertex LLMs.

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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-news-classification.js:20, tag aiplatform_sdk_classify_news_items

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[telpirion]

issue: I would remove any content that is potentially copyrighted, trademarked, or mentions a celebrity.

Remove mentions of Federer, Nadals, Tom Cruise, Mission Impossible, CNBC.

[gericdong]

Agreed. Changed.