[examples/seq2seq]: add --label_smoothing option (#5919)

examples/seq2seq/callbacks.py

@@ -5,7 +5,7 @@ from pathlib import Path
 import numpy as np
 import pytorch_lightning as pl
 import torch
-from pytorch_lightning.callbacks import ModelCheckpoint
+from pytorch_lightning.callbacks import EarlyStopping, ModelCheckpoint
 from pytorch_lightning.utilities import rank_zero_only
 
 
@@ -90,3 +90,7 @@ def get_checkpoint_callback(output_dir, metric):
         period=0,  # maybe save a checkpoint every time val is run, not just end of epoch.
     )
     return checkpoint_callback
+
+
+def get_early_stopping_callback(metric, patience):
+    return EarlyStopping(monitor=f"val_{metric}", mode="max", patience=patience, verbose=True,)