Add dice per label metric to segmentation bundles

[AHarouni]

Is your feature request related to a problem? Please describe.
In segmentation tasks the user would need ot

Describe the solution you'd like
we should add this in the val section

        "additional_metrics": {
            "val_dice_lb": {
                "_target_": "MeanDice",
                "include_background": true,
                "output_transform": "$monai.handlers.from_engine(['pred', 'label'])",
                "num_classes": "@output_classes",
                "return_with_label": true,
                "reduction": "mean_batch"
            }
        },
        "evaluator": {
            "_target_": "SupervisedEvaluator",
            "device": "@device",
            "val_data_loader": "@validate#dataloader",
            "network": "@network",
            "inferer": "@validate#inferer",
            "postprocessing": "@validate#postprocessing",
            "key_val_metric": "@validate#key_metric",
            "additional_metrics": "@validate#additional_metrics",
            "val_handlers": "@validate#handlers",
            "amp": true
        }