support qwen2-vl-2b lora finetune

[sunnychenxiwang]

support qwen2-vl lora finetue
1.update file 'paddlemix/examples/qwen2_vl/qwen2vl_finetune.py' to support lora finetune
2.add new file 'paddlemix/examples/qwen2_vl/shell/basline_2b_lora_bs32_1e8.sh'
3.update file 'paddlemix/examples/qwen2_vl/README.md'

[paddle-bot]

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