cherrypick extensions to start v1

proxy/pkg/flagset/flagset.go

@@ -30,6 +30,10 @@ func RootWithConfig(cfg *config.Config) []cli.Flag {
 			EnvVars:     []string{"PROXY_LOG_COLOR", "OCIS_LOG_COLOR"},
 			Destination: &cfg.Log.Color,
 		},
+		&cli.StringFlag{
+			Name:  "extensions",
+			Usage: "Run specific extensions during supervised mode",
+		},
 	}
 }