docs: Add Batch API tutorial

[InjunPark-sap]

What's changed

Add the LLM Batch API tutorial (batch_api.mdx) to the JS docs sidebar.

The tutorial document (docs-js/tutorials/batch_api.mdx) already existed but was not registered in sidebarsDocsJs.js, so it was not visible in local development or production builds.

Changes

• Add tutorials/using-llm-batch-api to the Tutorials category in sidebarsDocsJs.js

[InjunPark-sap]

docs: Update batch-api tutorial

Changes

docs-js/tutorials/batch-api.mdx

• Updated all method names to match the regenerated spec (batchServiceController... → listBatches, createBatch, etc.)
• AI-Resource-Group is now passed as a direct method parameter instead of .addCustomHeaders()
• Step 5: replaced S3 SDK download approach with FileApi.fileDownload() from @sap-ai-sdk/ai-api
• Added :::note in Introduction: Batch API currently supports Azure OpenAI models only
• Removed @aws-sdk/client-s3 from the upload info box (rclone/s3fs-fuse only)
• Added getBatchById() to the Manage Batch Jobs section

docs-js/foundation-models/openai/batch.mdx (new file)

• Added a concise API reference page under Foundation Models > OpenAI
• Covers: create job, poll status, download output with FileApi, and job management
• Marked as :::experimental