Fix bug where destroying a namespace would not always destroy projects

There is a race condition in DestroyGroupService now that projects are deleted asynchronously:

1. User attempts to delete group
2. DestroyGroupService iterates through all projects and schedules a Sidekiq job to delete each Project
3. DestroyGroupService destroys the Group, leaving all its projects without a namespace
4. Projects::DestroyService runs later but the can?(current_user,
   :remove_project) is `false` because the user no longer has permission to
   destroy projects with no namespace.
5. This leaves the project in pending_delete state with no namespace/group.

Projects without a namespace or group also adds another problem: it's not possible to destroy the container
registry tags, since container_registry_path_with_namespace is the wrong value.

The fix is to destroy the group asynchronously and to run execute directly on Projects::DestroyService.

Closes #17893

1 files changed, 2 insertions, 0 deletions

diff --git a/app/models/namespace.rb b/app/models/namespace.rb
index 8b52cc824cd..7c29d27ce97 100644
--- a/app/models/namespace.rb
+++ b/app/models/namespace.rb
@@ -1,4 +1,6 @@
 class Namespace < ActiveRecord::Base
+  acts_as_paranoid
+
   include Sortable
   include Gitlab::ShellAdapter