feat(genai): add Gemini batch prediction samples

[Sita04]

Description

Add Gemini Batch Prediction samples for GCS and BigQuery.

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)
• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• ai-platform/snippets/batch-prediction/batch-predict-bq.js:20, tag generativeaionvertexai_batch_predict_gemini_createjob_bigquery
• ai-platform/snippets/batch-prediction/batch-predict-gcs.js:20, tag generativeaionvertexai_batch_predict_gemini_createjob_gcs

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[Sita04]

Test build fails due to unrelated samples.

All tests for this PR passed:
Batch predict with Gemini ✔ should create Batch prediction Gemini job with GCS (6466ms) ✔ should create Batch prediction Gemini job with BigQuery (6387ms)