Mopve cache_util to OSS pattern 2

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/254

WTTS

Reviewed By: wat3rBro

Differential Revision: D36438060

fbshipit-source-id: 440daa5d238e7902606b3709ec7887260f1a20ec

d2go/data/cache_util.py

@@ -3,7 +3,10 @@
 
 import os
 
+from d2go.utils.oss_helper import fb_overwritable
 
+
+@fb_overwritable()
 def _cache_json_file(json_file):
     # TODO: entirely rely on PathManager for caching
     json_file = os.fspath(json_file)