[Omnibus] Deprecate Sidekiq min-concurrency and max-concurrency

What does this MR do?

Deprecate the sidekiq['min_concurrency'] and sidekiq['max_concurrency'] in favor of the new sidekiq['concurrency'].

See gitlab-com/gl-infra/scalability#2760 (closed)

‼ This MR has to be coordinated with the sidekiq-cluster release gitlab!143329 (merged) for 16.9

Related issues

• gitlab-com/gl-infra/scalability#2760 (closed)
• Deprecation issue: gitlab#439687 (closed)

Deprecation schedule

Configuration Key	Deprecation Date	Removal Date
sidekiq['min_concurrency']	%16.9	%17.0
sidekiq['max_concurrency']	%16.9	%17.0

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on the dev.gitlab.org mirror for this branch if the change is touching anything besides documentation or internal cookbooks. Please note that feature branches are not automatically mirrored to dev.gitlab.org, and should be manually pushed whenever necessary.
• trigger-package has a green pipeline running against latest commit
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated ( gitlab!143927 (merged))
• Tests updated
• Equivalent MR/issue for the GitLab Chart opened (not relevant, Helm charts only support 1 concurrency value which is used in CNG here, so we don't have to change GitLab charts.)
• Notify Product for inclusion in release notes