ClearML best practice to create a draft pipeline to have the task on the server so that it can be cloned, modified and executed at any time?

Well it is, we just assume that you executed the pipeline somewhere (i.e. made sure it works) 🙂

Correction:
What you actually are looking for (and I will make sure we have it in the doc) is :
pipeline.start(queue=None)It will just leave it as is, so you can manually enqueue / clone it 🙂