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 run `execute` directly on Projects::DestroyService.
 
Closes #17893

See merge request !4341

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

DRY code + fix rubocop

Add more test cases

Append to changelog

DRY changes list

find_url service for merge_requests

use GET for getting merge request links

remove files

rename to get_url_service

reduce loop

add test case for cross project

refactor tiny thing

update changelog

This change simplifies a Pipeline processing by introducing a special new status: created.
This status is used for all builds that are created for a pipeline.
We are then processing next stages and queueing some of the builds (created -> pending) or skipping them (created -> skipped).
This makes it possible to simplify and solve a few ordering problems with how previously builds were scheduled.
This also allows us to visualise a full pipeline (with created builds).

This also removes an after_touch used for updating a pipeline state parameters.
Right now in various places we explicitly call a reload_status! on pipeline to force it to be updated and saved.

Instead of redirecting from the project service to the service and back to the model,
put all destruction code in the service. Also removes a possible source of failure
where run_after_commit may not destroy the project.

Enable/Disable Deploy keys for a project

Closes #20123 

## Does this MR meet the acceptance criteria?

- [X] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [X] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [X] API support added
- Tests
  - [X] Added for this feature/bug
  - [X] All builds are passing

See merge request !5647