Fix owned account notes not being deleted when an account is deleted (#16579)

* Add account_notes relationship

* Add tests

* Fix owned account notes not being deleted when an account is deleted

* Add post-migration to clean up orphaned account notes

spec/services/delete_account_service_spec.rb

@@ -21,6 +21,8 @@ RSpec.describe DeleteAccountService, type: :service do
     let!(:favourite_notification) { Fabricate(:notification, account: local_follower, activity: favourite, type: :favourite) }
     let!(:follow_notification) { Fabricate(:notification, account: local_follower, activity: active_relationship, type: :follow) }
 
+    let!(:account_note) { Fabricate(:account_note, account: account) }
+
     subject do
       -> { described_class.new.call(account) }
     end
@@ -35,8 +37,9 @@ RSpec.describe DeleteAccountService, type: :service do
           account.active_relationships,
           account.passive_relationships,
           account.polls,
+          account.account_notes,
         ].map(&:count)
-      }.from([2, 1, 1, 1, 1, 1, 1]).to([0, 0, 0, 0, 0, 0, 0])
+      }.from([2, 1, 1, 1, 1, 1, 1, 1]).to([0, 0, 0, 0, 0, 0, 0, 0])
     end
 
     it 'deletes associated target records' do