Enable Bioimage Model Zoo pretrained models for training

[danifranco]

Add the option to retrain BMZ models, not just to do inference. There are two options we can do:

• Use Torchscript directly loaded models and work with that (possible errors in DDP? need to ensure all functionalities).
• Create a "regular" Pytorch model by calling the function that returns the model in the provided .py file (args are stored in the RDF), and then load pytorch_state_dict weigths. More complicated but this will ensure all functionalities of Pytorch