replace pytorch_lightning.metrics by torchmetrics for newer pytorch_lightning versions

[ghpu]

With pytorch_lightning 1.7 : ModuleNotFoundError: No module named 'pytorch_lightning.metrics'

Solution : change imports in python train_*.py from import pytorch_lightning.metrics.functional... into ```import torchmetrics.functional `` and install torchmetrics (pip install torchmetrics for example) .