store backup now in binary, and let backend serialize/deserialize

Software/MainBoard/rust/src/hal/esp.rs

@@ -749,10 +749,13 @@ impl Esp<'_> {
 
         let mut builder: McutieBuilder<'_, String, PublishDisplay<String, &str>, 0> =
             McutieBuilder::new(stack, "plant ctrl", mqtt_url);
-        if network_config.mqtt_user.is_some() && network_config.mqtt_password.is_some() {
+        if let (Some(mqtt_user), Some(mqtt_password)) = (
+            network_config.mqtt_user.as_ref(),
+            network_config.mqtt_password.as_ref(),
+        ) {
             builder = builder.with_authentication(
-                network_config.mqtt_user.as_ref().unwrap().as_str(),
-                network_config.mqtt_password.as_ref().unwrap().as_str(),
+                mqtt_user,
+                mqtt_password,
             );
             info!("With authentification");
         }