Allow a step to depend on (be triggered by) several other steps
This is needed for https://github.com/huggingface/datasets-server/issues/891.

And by the way, various steps already implicitly depend on various steps (they read the value of the cache for various steps). But their refresh is only triggered by one of them.


Allow a step to depend on (be triggered by) several other steps: This is needed for https://github.com/huggingface/datasets-server/issues/891.

And by the way, various steps already implicitly depend on various steps (they read the value of the cache for various steps). But their refresh is only triggered by one of them.

