Start monitoring server at benchmark tool

src/bin/bench_index.rs

@@ -31,6 +31,8 @@ fn run() -> Result<()> {
     let signal = Waiter::new();
     let config = Config::from_args();
     let metrics = Metrics::new(config.monitoring_addr);
+    metrics.start();
+
     let daemon = Daemon::new(config.network_type, &metrics)?;
     let fake_store = FakeStore {};
     let index = Index::load(&fake_store, &metrics);