Setup mail server and restructure some things

config/hosts/metrics/prometheus.nix

@@ -0,0 +1,19 @@
+{ hosts, ... }:
+{
+  services.prometheus = {
+    enable = true;
+    scrapeConfigs = [
+      {
+        job_name = "node";
+        static_configs = builtins.map (name: {
+          targets = [
+            "${name}.${hosts.${name}.site}.grzb.de:9100"
+          ];
+          labels = {
+            host = "${name}.${hosts.${name}.site}.grzb.de";
+          };
+        }) (builtins.attrNames hosts);
+      }
+    ];
+  };
+}