prometheus: proxy alert2muc thru nginx

hosts/prometheus/default.nix

@@ -43,6 +43,7 @@
       path_prefix = "/alertmanager";
     } {
       static_configs = [{
+        # alert2muc
         targets = [ "localhost:9022" ];
       }];
     }];
@@ -128,6 +129,9 @@
           auth_basic_user_file ${config.sops.secrets."nginx/httpAuth".path};
         '';
       };
+      locations."/alert2muc" = {
+        proxyPass = "http://localhost:9022";
+      };
     };
   };