updated the original RAG implementation to be compatible with latest Pytorch-Lightning (#11806)

* updated the original RAG implementation to be compatible with the latest PL version

* updated the requirements.txt file

* execute make style

* code quality test

* code quality

* conflix resolved in requirement.txt

* code quality

* changed the MyDDP class name to CustomDDP

examples/research_projects/rag/callbacks_rag.py

@@ -1,5 +1,4 @@
 import logging
-import os
 from pathlib import Path
 
 import numpy as np
@@ -34,9 +33,10 @@ def get_checkpoint_callback(output_dir, metric):
         )
 
     checkpoint_callback = ModelCheckpoint(
-        filepath=os.path.join(output_dir, exp),
+        dirpath=output_dir,
+        filename=exp,
         monitor=f"val_{metric}",
-        mode="max",
+        mode="min",
         save_top_k=3,
         period=1,  # maybe save a checkpoint every time val is run, not just end of epoch.
     )