Add redirect for field-update unset operation

Author: abinav2307

articles/cosmos-db/.openpublishing.redirection.cosmos-db.json

@@ -670,6 +670,11 @@
       "redirect_url": "/azure/cosmos-db/mongodb/vcore/operators/aggregation/$set",
       "redirect_document_id": true
     },
+    {
+      "source_path_from_root": "/articles/cosmos-db/mongodb/vcore/operators/field-update/$unset.md",
+      "redirect_url": "/azure/cosmos-db/mongodb/vcore/operators/aggregation/$unset",
+      "redirect_document_id": true
+    },
     {
       "source_path_from_root": "/articles/cosmos-db/nosql/troubleshoot-dot-net-sdk-request-timeout.md",
       "redirect_url": "/azure/cosmos-db/nosql/troubleshoot-dotnet-sdk-request-timeout",