Improve error message when no suitable file is found
See https://huggingface.co/datasets/wefussell/amasum_neg/discussions/1#654d1c3671a30c4bcaf9fb77

It contains the following tree:

<img width="647" alt="Capture d’écran 2023-11-09 à 19 36 17" src="https://github.com/huggingface/datasets-server/assets/1676121/0690bac7-c1fa-4737-9d66-1f717fb0311a">

The files have no extensions, so `datasets` cannot get the list of configs. But the error message mentions a dataset script. Now that we "deprecated" the datasets scripts in the dataset viewer, it's confusing for the users. The error message is:

```
Error code:   ConfigNamesError
Exception:    FileNotFoundError
Message:      Couldn't find a dataset script at /src/services/worker/wefussell/amasum_neg/amasum_neg.py or any data file in the same directory. Couldn't find 'wefussell/amasum_neg' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in wefussell/amasum_neg. 
Traceback:    Traceback (most recent call last):
                File "/src/services/worker/src/worker/job_runners/dataset/config_names.py", line 65, in compute_config_names_response
                  for config in sorted(get_dataset_config_names(path=dataset, token=hf_token))
                File "/src/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 351, in get_dataset_config_names
                  dataset_module = dataset_module_factory(
                File "/src/services/worker/.venv/lib/python3.9/site-packages/datasets/load.py", line 1508, in dataset_module_factory
                  raise FileNotFoundError(
              FileNotFoundError: Couldn't find a dataset script at /src/services/worker/wefussell/amasum_neg/amasum_neg.py or any data file in the same directory. Couldn't find 'wefussell/amasum_neg' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in wefussell/amasum_neg.
```

We should instead return an error message with a specific error code (different from "ConfigNamesError") so that the Hub can show a specific message, pointing to the [new docs](https://github.com/huggingface/hub-docs/pull/1070).
Improve error message when no suitable file is found: See https://huggingface.co/datasets/wefussell/amasum_neg/discussions/1#654d1c3671a30c4bcaf9fb77

It contains the following tree:

<img width="647" alt="Capture d’écran 2023-11-09 à 19 36 17" src="https://github.com/huggingface/datasets-server/assets/1676121/0690bac7-c1fa-4737-9d66-1f717fb0311a">

The files have no extensions, so `datasets` cannot get the list of configs. But the error message mentions a dataset script. Now that we "deprecated" the datasets scripts in the dataset viewer, it's confusing for the users. The error message is:

```
Error code:   ConfigNamesError
Exception:    FileNotFoundError
Message:      Couldn't find a dataset script at /src/services/worker/wefussell/amasum_neg/amasum_neg.py or any data file in the same directory. Couldn't find 'wefussell/amasum_neg' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in wefussell/amasum_neg. 
Traceback:    Traceback (most recent call last):
                File "/src/services/worker/src/worker/job_runners/dataset/config_names.py", line 65, in compute_config_names_response
                  for config in sorted(get_dataset_config_names(path=dataset, token=hf_token))
                File "/src/services/worker/.venv/lib/python3.9/site-packages/datasets/inspect.py", line 351, in get_dataset_config_names
                  dataset_module = dataset_module_factory(
                File "/src/services/worker/.venv/lib/python3.9/site-packages/datasets/load.py", line 1508, in dataset_module_factory
                  raise FileNotFoundError(
              FileNotFoundError: Couldn't find a dataset script at /src/services/worker/wefussell/amasum_neg/amasum_neg.py or any data file in the same directory. Couldn't find 'wefussell/amasum_neg' on the Hugging Face Hub either: FileNotFoundError: No (supported) data files or dataset script found in wefussell/amasum_neg.
```

We should instead return an error message with a specific error code (different from "ConfigNamesError") so that the Hub can show a specific message, pointing to the [new docs](https://github.com/huggingface/hub-docs/pull/1070).