Collect alertmanager metrics

services/monitoring/prometheus.nix

@@ -167,6 +167,14 @@
           }
         ];
       }
+      {
+        job_name = "alertmanager";
+        static_configs = [
+          {
+            targets = [ "localhost:9093" ];
+          }
+        ];
+      }
       {
         job_name = "pve-exporter";
         static_configs = [