Explain why loading config JSON fails
This PR improves the exception message thrown when reading configuration fails to include the information provided by the exception itself (line/column numbers, etc.). This can spare the reader of the message some trouble debugging it. See [this thread here](https://github.com/CompVis/stable-diffusion/issues/247) for background.
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_18964). All of your documentation changes will be reflected on that endpoint.<|||||>Could you just run the code quality tool to ensure that the code quality passes? You can install them with the following, from the root of your clone:
```
pip install -e ".[quality]"
```
And then run them with:
```
make fixup
```<|||||>@LysandreJik Yes, will do. Thank you!<|||||>@LysandreJik Sorry for the delay! I've applied the code quality changes.<|||||>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/main/CONTRIBUTING.md) are likely to be ignored.