grafana: disable signup, add provisioning

modules/services/grafana/module.nix

@@ -44,7 +44,28 @@ in {
           check_for_updates = false;
         };
 
-        # users.allow_signup = false;
+        users.allow_signup = false;
+      };
+      provision = {
+        enable = true;
+        datasources.settings = {
+          datasources = [
+            (mkIf config.modules.system.services.database.postgresql.enable {
+              name = "Prometheus";
+              type = "prometheus";
+              access = "proxy";
+              url = "http://127.0.0.1:4024";
+              isDefault = true;
+            })
+
+            (mkIf config.modules.system.services.prometheus.enable {
+              name = "PostgreSQL";
+              type = "postgres";
+              access = "proxy";
+              url = "http://127.0.0.1:${toString config.services.prometheus.port}";
+            })
+          ];
+        };
       };
     };
     services.nginx = {