Add `model_config = ConfigDict(use_attribute_docstrings=True)` when the command option `--use-field-description` is used

[9ao9ai9ar]

The use_attribute_docstrings key is available in Pydantic v2.7+ that enables docstrings of attributes to be used for field descriptions. If the value is the default False, the examples in the linked documentation would print None. It'll be nice for the docstrings to still be accessible via Model.model_fields["x"].description, just like if it's defined using Field(description="Description in Field").