Support case-insensitive Hub dataset name in load_dataset
### Feature request

The dataset name on the Hub is case-insensitive (see https://github.com/huggingface/moon-landing/pull/2399, internal issue), i.e., https://huggingface.co/datasets/GLUE redirects to https://huggingface.co/datasets/glue.

Ideally, we could load the glue dataset using the following:

```
from datasets import load_dataset
load_dataset('GLUE', 'cola')
```

It breaks because the loading script `GLUE.py` does not exist (`glue.py` should be selected instead).

Minor additional comment: in other cases without a loading script, we can load the dataset, but the automatically generated config name depends on the casing:
- `load_dataset('severo/danish-wit')` generates the config name `severo--danish-wit-e6fda5b070deb133`, while
- `load_dataset('severo/danish-WIT')` generates the config name `severo--danish-WIT-e6fda5b070deb133`

### Motivation

To follow the same UX on the Hub and in the datasets library.

### Your contribution

...
Closing as case-insensitivity should be only for URL redirection on the Hub. In the APIs, we will only support the canonical name (https://github.com/huggingface/moon-landing/pull/2399#issuecomment-1382085611)