add configuration options to enable mqtt user login

rust/src/hal/esp.rs

@@ -419,6 +419,8 @@ impl Esp<'_> {
             }),
             client_id: Some("plantctrl"),
             keep_alive_interval: Some(Duration::from_secs(60 * 60 * 2)),
+            username: network_config.mqtt_user.as_ref().map(|v| &**v),
+            password: network_config.mqtt_password.as_ref().map(|v| &**v),
             //room for improvement
             ..Default::default()
         };