Set the epoch timestamp when uploading data to dynamoDB (#130273)

This is to move away the `_event_time` field from Rockset, which we cannot use when reimport the data
Pull Request resolved: https://github.com/pytorch/pytorch/pull/130273
Approved by: https://github.com/clee2000

tools/stats/upload_stats_lib.py

@@ -4,6 +4,8 @@ import gzip
 import io
 import json
 import os
+
+import time
 import zipfile
 from pathlib import Path
 from typing import Any, Callable, Dict, List, Optional
@@ -153,6 +155,9 @@ def upload_to_dynamodb(
         for doc in docs:
             if generate_partition_key:
                 doc["dynamoKey"] = generate_partition_key(repo, doc)
+            # This is to move away the _event_time field from Rockset, which we cannot use when
+            # reimport the data
+            doc["timestamp"] = int(round(time.time() * 1000))
             batch.put_item(Item=doc)