Add comments to metrics

To improve readability.

src/main.rs

@@ -434,9 +434,13 @@ async fn metrics(
     metrics: &State<WebhookeyMetrics>,
     config: &State<Config>,
 ) -> Option<String> {
+    // Are metrics configured?
     if let Some(metrics_config) = &config.metrics {
+        // Are metrics enabled?
         if metrics_config.enabled {
+            // Is a filter configured?
             if let Some(filter) = &metrics_config.ip_filter {
+                // Does the request match the filter?
                 if filter.validate(&address.ip()) {
                     return Some(get_metrics(metrics));
                 }