Allow enabling experimental sidekiq-cluster
We're moving to running Sidekiq cluster as a default in the future. This allows administrators to opt-in to the sidekiq cluster behaviour already.
This behaviour will copy the configuration of sidekiq to sidekiq-cluster. So it will respect concurrency and logging settings.
When enabling cluster for Sidekiq, this will spin up a single
Sidekiq-cluster and Sidekiq process. Sidekiq-cluster will be
configured with the queue groups set to [*]. Which will spin up a
single Sidekiq process picking up all queues.
The documentation for this is being worked on in gitlab!27354 (merged)
Required for !4006 (merged)