[Enhance] Use opencv-python-headless by default

[HAOCHENYE]

This is only a workaround for

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/cpfs01/user/yehaochen/miniconda3/envs/py312torch28-6/lib/python3.12/site-packages/cv2/__init__.py", line 181, in <module>
    bootstrap()
  File "/cpfs01/user/yehaochen/miniconda3/envs/py312torch28-6/lib/python3.12/site-packages/cv2/__init__.py", line 153, in bootstrap
    native_module = importlib.import_module("cv2")
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/cpfs01/user/yehaochen/miniconda3/envs/py312torch28-6/lib/python3.12/importlib/__init__.py", line 90, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ImportError: libGL.so.1: cannot open shared object file: No such file or directory

when installing mmengine in ngc docker image. It’s not ideal; it’s purely to simplify internal use.

Motivation

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Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDetection or MMPretrain.
4. The documentation has been modified accordingly, like docstring or example tutorials.