Add notifications of severed relationships (#27511)

spec/fabricators/account_relationship_severance_event_fabricator.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+Fabricator(:account_relationship_severance_event) do
+  account
+  relationship_severance_event
+end

spec/fabricators/relationship_severance_event_fabricator.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+Fabricator(:relationship_severance_event) do
+  type { :domain_block }
+  target_name { 'example.com' }
+end

spec/fabricators/severed_relationship_fabricator.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+Fabricator(:severed_relationship) do
+  local_account { Fabricate.build(:account) }
+  remote_account { Fabricate.build(:account) }
+  relationship_severance_event { Fabricate.build(:relationship_severance_event) }
+  direction { :active }
+end