A new test to check config attributes being used
# What does this PR do?

Add a new test to check config attributes being used.

For edge cases, I only add rules to 2 files. If the concept is approved,  **I will add more to pass CI**, and continue the work of cleaning up in follow-up PR(s).
_The documentation is not available anymore as the PR was closed or merged._<|||||>@sgugger Ready for review - The failing tests will be addressed (by adding specific rules in subclasses) once the PR is approved 🙏 .<|||||>The report looks like (if unused attributes are detected)
```bash
ValueError: The following configuration classes contain unused attributes in the corresponding modeling files:
CLIPSegConfig: ['decoder_attention_dropout', 'decoder_hidden_act']
...
DinatConfig: ['patch_norm']
...
```<|||||>> Thanks for iterating! Just left a couple more comments.
> 
> As you noticed the job is failing right now, are you planning to add everything in the special map or to fix all the attributes not used?

Yes, that's mentioned in the description/comment (in previous version, it's better doing so, but with this new version you suggested, I can indeed add them earlier though).

FYI: the special map I will update will contain
- some confirmed allowed cases (i.e. we know the reasons and nothing we can do but just allow)
- some skipped cases **for now** to allow temporarily with #TODO comment<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_21453). All of your documentation changes will be reflected on that endpoint.