Fix ph_key issue with trec pipeline (#2363)

Summary:
Pull Request resolved: #2363

Fix ph_key issue by:
1. make ph_key for TrainModelInput to be model_input.id_list_features["defalut"]
2. handles parsing in trec utils.

Reviewed By: malaybag

Differential Revision: D62160686

fbshipit-source-id: 5795926021e591fa72e23a32f8050c898da641fb

Author: Ruilin Chen

torchrec/distributed/train_pipeline/utils.py

@@ -777,7 +777,8 @@ def _get_node_args_helper(
                     # pyre-ignore[16]
                     ph_key: str = child_node.ph_key
                     # example: ph_key = 'event_id_list_features_seqs[marketplace]'
-                    ph_keys = ph_key.split("[")
+                    ph_key = ph_key.replace("[", ".")
+                    ph_keys = ph_key.split(".")
                     for key in ph_keys:
                         if "]" in key:
                             arg_info.input_attrs.append(key[:-1])