Add notification policies and notification requests (#29366)

app/serializers/rest/notification_request_serializer.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class REST::NotificationRequestSerializer < ActiveModel::Serializer
+  attributes :id, :created_at, :updated_at, :notifications_count
+
+  belongs_to :from_account, key: :account, serializer: REST::AccountSerializer
+  belongs_to :last_status, serializer: REST::StatusSerializer
+
+  def id
+    object.id.to_s
+  end
+
+  def notifications_count
+    object.notifications_count.to_s
+  end
+end