FEATURE: Converge on (part) of the TaskDocument

[davidwaroquiers]

In order to be able to use "code-agnostic-like" workflows, we should try to converge on some parts of the TaskDocument's. One obvious example is the finite-difference elastic constants workflow where the deformations could be performed using "any" code, provided the response follows some convention, i.e. it should have the energy, the forces, stress, ... This needs some discussions with @utf on how to deal with that. We might consider having some general pydantic models that are subclassed for the different codes (somewhat similar to StructureMetadata).