Add notification policies and notification requests (#29366)

app/serializers/rest/notification_policy_serializer.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class REST::NotificationPolicySerializer < ActiveModel::Serializer
+  attributes :filter_not_following,
+             :filter_not_followers,
+             :filter_new_accounts,
+             :filter_private_mentions,
+             :summary
+
+  def summary
+    {
+      pending_requests_count: object.pending_requests_count.to_s,
+      pending_notifications_count: object.pending_notifications_count.to_s,
+    }
+  end
+end