(torchx/cli) allow the default scheduler to be specified via .torchxconfig (#506)

Summary:
Pull Request resolved: #506

Lets users specify their choice of default scheduler via `.torchxconfig` (similar to how they can specify the default component in `.torchxconfig`)

Reviewed By: d4l3k, dragonxlwang

Differential Revision: D36849694

fbshipit-source-id: 9d32d928629a2e7f9b781ef76eba050fa6b43060

Author: Kiuk Chung

torchx/cli/cmd_run.py

@@ -122,8 +122,9 @@ def add_arguments(self, subparser: argparse.ArgumentParser) -> None:
             "-s",
             "--scheduler",
             type=str,
-            help=f"Name of the scheduler to use. One of: [{','.join(scheduler_names)}]",
             default=get_default_scheduler_name(),
+            action=torchxconfig_run,
+            help=f"Name of the scheduler to use. One of: [{','.join(scheduler_names)}]",
         )
         subparser.add_argument(
             "-cfg",