Endpoint respond by input type
Part of https://github.com/huggingface/datasets-server/issues/755
This change will allow endpoints respond based on input type having a list of processing steps 
e.g:
- /splits with dataset param will reach out to /splits cache kind
- /splits with config param will reach out to /splits-from-streaming first and then /splits-form-dataset-info

Endpoint respond by input type: Part of https://github.com/huggingface/datasets-server/issues/755
This change will allow endpoints respond based on input type having a list of processing steps 
e.g:
- /splits with dataset param will reach out to /splits cache kind
- /splits with config param will reach out to /splits-from-streaming first and then /splits-form-dataset-info
