[api request] API to obtain "dataset_module" dynamic path?
**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is.

This is an awesome library. 

It seems like the dynamic module path in this library has broken some of hyperparameter tuning functionality: https://discuss.huggingface.co/t/using-hyperparameter-search-in-trainer/785/34

This is because Ray will spawn new processes, and each process will load modules by path. However, we need to explicitly inform Ray to load the right modules, or else it will error upon import. 

I'd like an API to obtain the dynamic paths. This will allow us to support this functionality in this awesome library while being future proof.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

`datasets.get_dynamic_paths -> List[str]` will be sufficient for my use case.

By offering this API, we will be able to address the following issues (by patching the ray integration sufficiently):

https://github.com/huggingface/blog/issues/106
https://github.com/huggingface/transformers/issues/11565
https://discuss.huggingface.co/t/using-hyperparameter-search-in-trainer/785/34
https://discuss.huggingface.co/t/using-hyperparameter-search-in-trainer/785/35


Hi @richardliaw, 

First, thanks for the compliments.

In relation with your request, currently, the dynamic modules path is obtained this way:
```python
from datasets.load import init_dynamic_modules, MODULE_NAME_FOR_DYNAMIC_MODULES

dynamic_modules_path = init_dynamic_modules(MODULE_NAME_FOR_DYNAMIC_MODULES)
```

Let me know if it is OK for you this way. 

I could set `MODULE_NAME_FOR_DYNAMIC_MODULES` as default value, so that you could instead obtain the path with:
```
dynamic_modules_path = datasets.load.init_dynamic_modules()
``` Hi @albertvillanova, the default value proposal seems great :) Looking forward to this! I like the idea as well ! thanks @albertvillanova  Hi @richardliaw, the feature is on the master branch and will be included in the next release in a couple of weeks. awesome work @albertvillanova !