Skip defering scheduled jobs in concurrency limit client middleware

What does this MR do and why?

Skip defering scheduled jobs in concurrency limit client middleware

This commit adds a check to omit Sidekiq scheduled jobs from the concurrency limit client middleware checks. These jobs can be checked and deferred when they are enqueued.

Fixes a functional bug where scheduled jobs are deferred and enqueued using .perform_async. This could result in the job being performed before its intended schedule.

Related to gitlab-com/gl-infra/scalability#3877

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Before	After

How to set up and validate locally

1. Apply this diff

diff --git a/app/workers/chaos/sleep_worker.rb b/app/workers/chaos/sleep_worker.rb
index 149bab5d9d3c..1ad62b51e7ea 100644
--- a/app/workers/chaos/sleep_worker.rb
+++ b/app/workers/chaos/sleep_worker.rb
@@ -6,6 +6,8 @@ class SleepWorker # rubocop:disable Scalability/IdempotentWorker
 
     data_consistency :always
 
+    concurrency_limit -> { 1 }
+
     sidekiq_options retry: 3
     include ChaosQueue

2. Restart gdk and open a console

➜  gitlab git:(sc1-fix-climit-scheduled-jobs) ✗ gdk restart rails
ok: down: /Users/sylvesterchin/work/gitlab-development-kit/services/rails-background-jobs: 1s
ok: down: /Users/sylvesterchin/work/gitlab-development-kit/services/rails-web: 0s
ok: run: /Users/sylvesterchin/work/gitlab-development-kit/services/rails-background-jobs: (pid 76221) 0s, normally down
ok: run: /Users/sylvesterchin/work/gitlab-development-kit/services/rails-web: (pid 76220) 0s, normally down

3. Run (0..40).map { Chaos::SleepWorker.perform_async(2) } a bunch of times until you exceed the concurrency. You should see nil once that happens.

[6] pry(main)> x = (0..40).map { Chaos::SleepWorker.perform_async(2) }
=> ["e3df4dc34d89ba698911fd51",
 "6aa606d546ba1e8daab1a165",
 "750183fda330d0b0c443cfa9",
 nil,
 nil,
 nil,
 nil,
 nil,
 nil,
 nil,
...]

4. Run a schedule job

On this branch, you should get a job id indicating that it is scheduled.

[7] pry(main)> Chaos::SleepWorker.perform_in(100,3)
=> "95cf5961c914b64908b50ed9"

On the master branch (run gdk restart and possibly step 3), you will get a nil, indicating that it is deferred.

[7] pry(main)> Chaos::SleepWorker.perform_in(100,3)
=> nil