scripts: make --service a required argument

Drop the implicit Service.Core default for --service in update_config_and_restart_nodes
and require it explicitly, so the targeted service is always a conscious choice
rather than silently defaulting to Core.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: matanl-starkware

scripts/prod/update_config_and_restart_nodes.py

@@ -138,11 +138,10 @@ def main():
         "--service",
         type=service_type_converter,
         choices=list(Service),
-        default=Service.Core,
+        required=True,
         metavar="SERVICE",
         help="Service type to operate on; determines configmap and pod names. One of: "
-        + ", ".join(str(service) for service in Service)
-        + " (default: Core)",
+        + ", ".join(str(service) for service in Service),
     )
 
     args_builder.add_argument(