add cg ls, prepare for rc subcommands

src/bin/dkl.rs

@@ -81,6 +81,16 @@ enum Command {
         #[arg(long, default_value = "5s")]
         timeout: Duration,
     },
+
+    Cg {
+        #[command(subcommand)]
+        cmd: CgCmd,
+    },
+}
+
+#[derive(Subcommand)]
+enum CgCmd {
+    Ls,
 }
 
 #[tokio::main(flavor = "current_thread")]
@@ -157,6 +167,10 @@ async fn main() -> Result<()> {
         .run()
         .await
         .map(|_| ())?),
+
+        C::Cg { cmd } => match cmd {
+            CgCmd::Ls => Ok(dkl::cgroup::ls().await?),
+        },
     }
 }