Trouble loading image folder with additional features -  metadata file ignored
I reproduced too:
- root: metadata file is ignored (https://huggingface.co/datasets/severo/doc-image-3)
- data/ dir: metadata file is ignored (https://huggingface.co/datasets/severo/doc-image-4)
- train/ dir: works (https://huggingface.co/datasets/severo/doc-image-5)
### Describe the bug

Loading image folder with a caption column using `load_dataset(<image_folder_path>)` doesn't load the captions. 

When loading a local image folder with captions using `datasets==2.13.0`
```
from datasets import load_dataset
data = load_dataset(<image_folder_path>)
data.column_names
```
yields 
`{'train': ['image', 'prompt']}`

but when using `datasets==2.15.0`
yeilds 
`{'train': ['image']}`

Putting the images and `metadata.jsonl` file into a nested `train` folder **or** loading with `load_dataset("imagefolder", data_dir=<image_folder_path>)` solves the issue and
yields 
`{'train': ['image', 'prompt']}`

### Steps to reproduce the bug

1. create a folder `<image_folder_path>` that contains images and a metadata file with additional features- e.g. "prompt"
2. run:
```
from datasets import load_dataset
data = load_dataset("<image_folder_path>")
data.column_names
```

### Expected behavior

`{'train': ['image', 'prompt']}`

### Environment info

- `datasets` version: 2.15.0
- Platform: Linux-5.15.120+-x86_64-with-glibc2.35
- Python version: 3.10.12
- `huggingface_hub` version: 0.19.4
- PyArrow version: 9.0.0
- Pandas version: 1.5.3
- `fsspec` version: 2023.6.0