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

The `non_archived` scope applied here
https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/controllers/conc
erns/issues_action.rb#L5 overrides the previous `ORDER BY` applied
inside the IssuesFinder, with the default scope of the Project model,
resulting in SQL errors.

The route is supposed to redirect the Groups#index request based on
whether or not a user was logged in. If they are, we redirect them to
their groups dashboard; if they're not, we redirect them to the public
Explore page.

But due to overly aggressive `before_action`s that weren't excluding the
`index` action, the request always resulted in a 404, whether a user was
logged in or not.

Closes #12660