NAT-315: Restore ISIS should be optional in migrate iptrunk

gso/workflows/iptrunk/migrate_iptrunk.py

@@ -578,6 +578,8 @@ def migrate_iptrunk() -> StepList:
 
     TODO: add interface checks
     """
+    should_restore_isis_metric = conditional(lambda state: state["restore_isis_metric"])
+
     return (
         init
         >> store_process_subscription(Target.MODIFY)