Add “services” and “metadata” to NodeInfo (#18563)

* add services to NodeInfo response

* add metadata to NodeInfo response

* learning ruby syntax!

* patch the patch

* rm trailing whitespace

* use [] instead of empty array constructor

app/serializers/nodeinfo/serializer.rb

@@ -3,7 +3,7 @@
 class NodeInfo::Serializer < ActiveModel::Serializer
   include RoutingHelper
 
-  attributes :version, :software, :protocols, :usage, :open_registrations
+  attributes :version, :software, :protocols, :services, :usage, :open_registrations, :metadata
 
   def version
     '2.0'
@@ -37,6 +37,10 @@ class NodeInfo::Serializer < ActiveModel::Serializer
     Setting.registrations_mode != 'none' && !Rails.configuration.x.single_user_mode
   end
 
+  def metadata
+    []
+  end
+
   private
 
   def instance_presenter