Update work items traversal ids after group and project transfer

What does this MR do and why?

Add workers to handle updating work items traversal ids when transferring a project or a group.

More info on the namespace_traversal_ids initiative: https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/traversal_ids_on_issues/

Database Queries

• Initial IID
• Next IID
• Update

References

Screenshots or screen recordings

A sub-group and its project gets moved to another group and the traversal IDs get updated:

Screen_Recording_2025-09-09_at_09.29.29

Before	After

How to set up and validate locally

1. Enable the feature flag Feature.enable(:update_work_item_traversal_ids_on_transfer)
2. See the current traversal IDs of the group/project

   n = Namespace.find_by_path('YOUR_GROUP_PATH')
   n.traversal_ids # => [...]

3. Likely the work items in that group don't have a traversal_ids set if they're older (we didn't backfill them yet). But you can query them via:

   n.work_items.first.namespace_traversal_ids

4. Go to a group's or project's settings http://gdk.test:3000/groups/YOUR_GROUP_PATH/-/edit
5. In the Advanced Section, select another group you want to transfer the project/group to
6. Transfer it and then check the traversal IDs again (ensure that your Sidekiq jobs are working - a full restart when checking out the branch helps)

   n.work_items.first.namespace_traversal_ids # => should output the new traversal_ids

When you choose a group, it also updated the traversal_ids of the descendent namespaces.

MR acceptance checklist

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Related to #562317 (closed)