Delete container repository tags outside of transaction

When there are many tags in a container repository, deleting them
can exceed the default 60 second idle-in-transaction timeout in
Sidekiq. We now explicitly delete them in the DestroyService
before destroying the model.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51380

app/services/projects/container_repository/destroy_service.rb

@@ -6,6 +6,8 @@ module Projects
       def execute(container_repository)
         return false unless can?(current_user, :update_container_image, project)
 
+        # Delete tags outside of the transaction to avoid hitting an idle-in-transaction timeout
+        container_repository.delete_tags!
         container_repository.destroy
       end
     end

changelogs/unreleased/sh-delete-tags-outside-transaction.yml

+---
+title: Delete container repository tags outside of transaction
+merge_request: 21679
+author:
+type: fixed

spec/features/container_registry_spec.rb

@@ -39,7 +39,7 @@ describe "Container Registry", :js do
       visit_container_registry
 
       expect_any_instance_of(ContainerRepository)
-        .to receive(:delete_tags!).and_return(true)
+        .to receive(:delete_tags!).twice.and_return(true)
 
       click_on(class: 'js-remove-repo')
     end

spec/services/projects/container_repository/destroy_service_spec.rb

@@ -33,6 +33,7 @@ describe Projects::ContainerRepository::DestroyService do
       end
 
       it 'deletes the repository' do
+        expect(repository).to receive(:delete_tags!).twice.and_call_original
         expect { described_class.new(project, user).execute(repository) }.to change { ContainerRepository.all.count }.by(-1)
       end
     end