default config name doesn't work when config kwargs are specified.
### Describe the bug

https://github.com/huggingface/datasets/blob/12cfc1196e62847e2e8239fbd727a02cbc86ddec/src/datasets/builder.py#L518-L522

If `config_name` is `None`, `DEFAULT_CONFIG_NAME` should be select. But once users pass `config_kwargs` to their customized `BuilderConfig`, the logic is ignored, and dataset cannot select the default config from multiple configs.

### Steps to reproduce the bug

```python
import datasets

datasets.load_dataset('/dataset/with/multiple/config'')  # Ok
datasets.load_dataset('/dataset/with/multiple/config', some_field_in_config='some')  # Err
```

### Expected behavior

Default config behavior should be consistent.

### Environment info

- `datasets` version: 2.14.3
- Platform: Linux-5.15.0-76-generic-x86_64-with-glibc2.17
- Python version: 3.8.15
- Huggingface_hub version: 0.16.4
- PyArrow version: 12.0.1
- Pandas version: 1.5.3