Add a feature flag to disable deduplication

What does this MR do?

This adds a feature flag allowing us to stop the automatic deduplication of queues.

This gives us a way out if we were to find bugs caused by deduplicating idempotent jobs.

gitlab-com/gl-infra/scalability#327

Does this MR meet the acceptance criteria?

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

• [ x Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done