Move WorkerAttributes to the right directory

What does this MR do?

This is a concern that is included in all workers through the ApplicationWorker. So I think it should live in app/workers/concerns.

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• [-] Code review guidelines
• [-] Merge request performance guidelines
• [-] Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers