As part of the work related to
https://gitlab.com/gitlab-org/gitlab/-/issues/218526 we have simplified
the use of issue_trackers and external_issue_trackers.

For more information see the related merge requests:
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/32330
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/33263
- https://gitlab.com/gitlab-org/gitlab/-/merge_requests/36063