Add notifications of severed relationships (#27511)

app/serializers/rest/account_relationship_severance_event_serializer.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class REST::AccountRelationshipSeveranceEventSerializer < ActiveModel::Serializer
+  attributes :id, :type, :purged, :target_name, :created_at
+
+  def id
+    object.id.to_s
+  end
+end

app/serializers/rest/notification_serializer.rb

@@ -6,6 +6,7 @@ class REST::NotificationSerializer < ActiveModel::Serializer
   belongs_to :from_account, key: :account, serializer: REST::AccountSerializer
   belongs_to :target_status, key: :status, if: :status_type?, serializer: REST::StatusSerializer
   belongs_to :report, if: :report_type?, serializer: REST::ReportSerializer
+  belongs_to :relationship_severance_event, key: :event, if: :relationship_severance_event?, serializer: REST::AccountRelationshipSeveranceEventSerializer
 
   def id
     object.id.to_s
@@ -18,4 +19,8 @@ class REST::NotificationSerializer < ActiveModel::Serializer
   def report_type?
     object.type == :'admin.report'
   end
+
+  def relationship_severance_event?
+    object.type == :severed_relationships
+  end
 end