Remove duplicate addition of callbacks/make optional

[romeokienzler]

in cli_tools.py:

        parser.add_lightning_class_args(StateDictAwareModelCheckpoint, "ModelCheckpoint")
        parser.set_defaults({"ModelCheckpoint.filename": "{epoch}", "ModelCheckpoint.monitor": "val/loss"})

        parser.add_lightning_class_args(StateDictAwareModelCheckpoint, "StateDictModelCheckpoint")
        parser.set_defaults(
            {
                "StateDictModelCheckpoint.filename": "{epoch}_state_dict",
                "StateDictModelCheckpoint.save_weights_only": True,
                "StateDictModelCheckpoint.monitor": "val/loss",
            }
        )

We need to check if it makes sense to have both callbacks added at the same time, also need to remove those if the config already provides those

@paolofraccaro