Add example on LLM offline inference

[JasonLo]

This example may be valuable for:

• Generating large volumes of synthetic data with open-source LLMs.
• Performing large-scale, structured data extraction from text.
• Embedding extensive text datasets.
• Cost-effectively executing LLM-driven tasks at scale without relying on expensive commercial solutions.

For more details, please refer to vllm_batch_inference/README.md.