introduce img_root_secondary to torchx macros (meta-pytorch#1060)

Summary: Pull Request resolved: meta-pytorch#1060

Differential Revision: D74093902

Author: burak-turk

torchx/specs/api.py

@@ -172,6 +172,7 @@ class macros:
     base_img_root = "${base_img_root}"
     app_id = "${app_id}"
     replica_id = "${replica_id}"
+    img_root_secondary = "${img_root_secondary}"
 
     # rank0_env will be filled with the name of the environment variable that
     # provides the master host address. To get the actual hostname the
@@ -187,6 +188,7 @@ class Values:
         replica_id: str
         rank0_env: str
         base_img_root: str = "DEPRECATED"
+        img_root_secondary: str = ""
 
         def apply(self, role: "Role") -> "Role":
             """