Rename old push_to_hub configs to "default" in dataset_infos
Fix

```python
from datasets import load_dataset_builder

b = load_dataset_builder("lambdalabs/pokemon-blip-captions", "default")
print(b.info)
```

which should return

```
DatasetInfo(
  features={'image': Image(decode=True, id=None), 'text': Value(dtype='string', id=None)}, 
  dataset_name='pokemon-blip-captions',
  config_name='default', 
  version=0.0.0,
  splits={'train': SplitInfo(name='train', num_bytes=119417410.0, num_examples=833, shard_lengths=None, dataset_name='pokemon-blip-captions')},
  download_checksums=None,
  download_size=99672355,
  dataset_size=119417410.0,
  size_in_bytes=219089765.0,
  ...
)
```

instead of and empty dataset info.

The dataset has a dataset_infos.json file with a deprecated config name "lambdalabs--pokemon-blip-captions". We switched those config names to "default" in 2.14, so the builder.info should take this into account.