Config overrides option working on any kind of config
# 🚀 Feature request

Allow the `--config_overrides` option in language-modeling examples to override a config that was specified by `--config_name` or `--model_name_or_path`, currently this is blocked by:
```python
if self.config_overrides is not None and (self.config_name is not None or self.model_name_or_path is not None):                                                    
            raise ValueError(                                                                                                                                              
                "--config_overrides can't be used in combination with --config_name or --model_name_or_path"                                                               
            )  
```

## Motivation

It is unclear why this is prevented, and it can make things a lot easier when tweaking the settings compared to having to edit a json file everytime. Is there a good reason for not allowing that?

## Your contribution

I can create a PR and make the changes myself.
If I remember correctly, it's because the transformers logic prevents us from overriding config if either of those 2 are defined.

I'm sure you will see it immediately if you remove the constraint.

If you find a good way to fix it, by all means please do.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.