Sidekiq troubeshooting - performance issues, and removing sidekiq-cluster Omnibus service from a 14.0+ instance

What does this MR do?

Testing and a customer ticket (link for GitLab team members) indicates it's possible to get stuck with a second (fully deprecated) sidekiq-cluster process along side sidekiq process on Omnibus 14.0 and higher.

Chef is unable to remove it as the code doesn't exist to manage this service.

Additionally, an approach for troubleshooting slow Sidekiq performance is added. Context for this addition can be found at #368685 (comment 1049678738)

Related issues

• sidekiq-cluster service might get left behind i... (omnibus-gitlab#6965 - closed)
• Improved Sidekiq troubleshooting strategies (#368685)

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