✨ NEW: Module: Workflows - Input validation

[mbercx]

Currently there is no explanation in the tutorial on how to add validation to the input ports. @flavianojs has already shown me that he was working on this, so I'll assign him to this issue for now.

One question here is whether this should be added on the CalcJob level or the WorkChain one. I think there is no real difference between them, but since we spend quite a bit of time on how to write workflows, perhaps it makes more sense to do this here.