feat(metrics): Add blackbox exporter

configuration/services/metrics/exporters.nix

@@ -10,6 +10,20 @@ in
 {
   services.prometheus = {
     exporters = {
+      blackbox = {
+        enable = true;
+        listenAddress = "127.0.0.1";
+        configFile = yaml.generate "blackbox.yaml" {
+          modules = {
+            http_2xx = {
+              prober = "http";
+              timeout = "5s";
+              http.preferred_ip_protocol = "ip4";
+            };
+          };
+        };
+      };
+
       # Periodically check domain registration status
       domain = {
         enable = true;
@@ -71,7 +85,6 @@ in
     # TODO(tlater):
     #   - wireguard (?)
     #   - postgres (?)
-    #   - blackbox (?) (curl to see if http and similar is up)
     #   - ssl_exporter (?)
   };
 }