Move predict config update from model loading to config validation

[francoishernandez]

Previously we had no choice than wait for the checkpoint to be loaded to grab its config, because everything was nested within a single .pt picke file.

Now that everything is nicely split in a directory structure, with directly accessible configuration files, we can move some of this logic to the config validation methods.

This brings two benefits:

• centralize more and more logic within config validation instead of it being scattered across the framework;
• grab the proper config sooner in the execution, preventing some unwanted behaviours.