[I/O] Model part names inconsistencies in ProjectParameters.json

[rubenzorrilla]

Description
Right now, our ProjecParameters.json mixes both full model part names (e.g. in the processes) with partial ones (e.g. in the solver_settings). This a legacy inconsistency coming from the times in which we didn't have the Model container.

The @KratosMultiphysics/technical-committee is of the opinion of unifying everything to use full names, of course taking into account backward compatibility. Nevertheless, we would like to hear the community's opinion on this regard.

[loumalouomega]

I hope we don't break up many things...

[RiccardoRossi]

@KratosMultiphysics/technical-committee decided to go forward with this change. The practical implication is that old cases will need to be slightly updated to add the full path in the ProjectParameters.json

This implies that the warnings that are currently issued should be transformed into errors. Whenever possible solvers should be modified to give suggestions to the users on how to modify the input, nevertheless please note that there is no way this can be enforced outside of the main applications