Iterate over `epic_issues` table and create corresponding records in the `work_item_parent_links` table. In order to sync `epic_issues` records into `work_item_parent_links` we need to find the corresponding `epics.issue_id` for every `epic_issues.epic_id` which would act as the `work_item_parent_links.work_item_parent_id` and `epic_issues.issue_id` would be mapped to `work_item_parent_links.work_item_id` This migration will have 2 parts: - Enqueue the backfilling migration - Finalise the backfilling migration This migration is blocked by https://gitlab.com/groups/gitlab-org/-/epics/12740+ migration as we need to make sure that every epic has a corresponding record in issues table.