add local file read path for image which could work with dataset like…

[sywangyi]

… Lin-Chen/ShareGPT4V

What does this PR do?

Fixes # (issue)

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[sywangyi]

python3 benchmark_serving.py --backend openai-chat --host 0.0.0.0 --port 80 --endpoint /v1/chat/completions --model Qwen/Qwen2-VL-7B-Instruct --dataset-path Lin-Chen/ShareGPT4V --dataset-name hf --hf-subset ShareGPT4V --hf-split train --num-prompts=1,
such command will fail, since tgi does not support file:// input for image now.
benchmark from https://github.com/vllm-project/vllm/tree/main/benchmarks

[sywangyi]

@Narsil pls help review