Create step `dataset-split-names`
See https://github.com/huggingface/datasets-server/issues/1014#issuecomment-1497597525

It aims at replacing `dataset-split-names-from-dataset-info` and `dataset-split-names-from-streaming`, now that one step can have two parents (or more)

Note the new method:

https://github.com/huggingface/datasets-server/blob/4e776c95799e23a6874ca1ebce0a1cfd7cb29e39/libs/libcommon/src/libcommon/simple_cache.py#L241-L267

It might be used in other places, for example in `service/api` instead of:

https://github.com/huggingface/datasets-server/blob/e89a249ac3dc7548517f8c516089b9f961258565/services/api/src/api/routes/endpoint.py#L52

Create step `dataset-split-names`: See https://github.com/huggingface/datasets-server/issues/1014#issuecomment-1497597525

It aims at replacing `dataset-split-names-from-dataset-info` and `dataset-split-names-from-streaming`, now that one step can have two parents (or more)

Note the new method:

https://github.com/huggingface/datasets-server/blob/4e776c95799e23a6874ca1ebce0a1cfd7cb29e39/libs/libcommon/src/libcommon/simple_cache.py#L241-L267

It might be used in other places, for example in `service/api` instead of:

https://github.com/huggingface/datasets-server/blob/e89a249ac3dc7548517f8c516089b9f961258565/services/api/src/api/routes/endpoint.py#L52
