Transient tasks

[bpiwowar]

Some tasks are just intermediaries, and could be marked as transient in an experimental plan

with experiment(...):
  # other option = TransientMode.TRANSIENT
  a = task_a.submit(transient=TransientMode.REMOVE)
  
  b1 = TaskB.C(a=a, x=1).submit()
  b2 = TaskB.C(a=a, x=2).submit()

When finishing the experiment, task_a job folder can be removed (if TransientMode.REMOVE). The other mode TRANSIENT (implied by REMOVE) has the following meaning: task_a is only run if required by another (non transient) task.