nixos/discourse: Update redis server settings...

...to match the updated redis module.

nixos/modules/services/web-apps/discourse.nix

@@ -656,7 +656,12 @@ in
       long_polling_interval = null;
     };
 
-    services.redis.enable = lib.mkDefault (cfg.redis.host == "localhost");
+    services.redis.servers.discourse =
+      lib.mkIf (lib.elem cfg.redis.host [ "localhost" "127.0.0.1" ]) {
+        enable = true;
+        bind = cfg.redis.host;
+        port = cfg.backendSettings.redis_port;
+      };
 
     services.postgresql = lib.mkIf databaseActuallyCreateLocally {
       enable = true;
@@ -697,12 +702,12 @@ in
     systemd.services.discourse = {
       wantedBy = [ "multi-user.target" ];
       after = [
-        "redis.service"
+        "redis-discourse.service"
         "postgresql.service"
         "discourse-postgresql.service"
       ];
       bindsTo = [
-        "redis.service"
+        "redis-discourse.service"
       ] ++ lib.optionals (cfg.database.host == null) [
         "postgresql.service"
         "discourse-postgresql.service"