[fix]: add __init__.py in examples pkg

[e06084]

to fix following error:

python examples/gradio_demo_chat.py --code_path=/mnt/bigdisk/qa_test_models/internlm/internlm-xcomposer2-vl-7b
Traceback (most recent call last):
  File "/mnt/bigdisk/chupei/code/InternLM-XComposer/examples/gradio_demo_chat.py", line 24, in <module>
    from examples.utils import auto_configure_device_map, get_stopping_criteria, set_random_seed
ModuleNotFoundError: No module named 'examples.utils'