Make sidekiq-cluster play well with Sidekiq 5.2.2+

Sidekiq 5.2.2 introduced a change
(https://github.com/mperham/sidekiq/pull/3936/files) that prevents queue
names from being duplicated. This breaks our current GitLab.com
config because we have some sidekiq-cluster processes configured
as the following:

```ruby
sidekiq_cluster['queue_groups'] = ["process_commit,process_commit"]
```

To keep things backwards compatible, we now only pass unique queue names
but scale the weights accordingly by the number of queues mentioned.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/54253

ee/changelogs/unreleased/sh-fix-sidekiq-cluster-5-2-3.yml

+---
+title: Make sidekiq-cluster play well with Sidekiq 5.2.2+
+merge_request: 8522
+author:
+type: other

ee/lib/gitlab/sidekiq_cluster.rb

@@ -70,14 +70,16 @@ module Gitlab
     #
     # Returns the PID of the started process.
     def self.start_sidekiq(queues, env, directory = Dir.pwd, max_concurrency = 50, dryrun: false)
+      counts = count_by_queue(queues)
+
       cmd = %w[bundle exec sidekiq]
       cmd << "-c #{self.concurrency(queues, max_concurrency)}"
       cmd << "-e#{env}"
-      cmd << "-gqueues: #{queues.join(', ')}"
+      cmd << "-gqueues: #{proc_details(counts)}"
       cmd << "-r#{directory}"
 
-      queues.each do |q|
-        cmd << "-q#{q},1"
+      counts.each do |queue, count|
+        cmd << "-q#{queue},#{count}"
       end
 
       if dryrun
@@ -97,6 +99,20 @@ module Gitlab
       pid
     end
 
+    def self.count_by_queue(queues)
+      queues.each_with_object(Hash.new(0)) { |element, hash| hash[element] += 1 }
+    end
+
+    def self.proc_details(counts)
+      counts.map do |queue, count|
+        if count == 1
+          queue
+        else
+          "#{queue} (#{count})"
+        end
+      end.join(', ')
+    end
+
     def self.concurrency(queues, max_concurrency)
       if max_concurrency.positive?
         [queues.length + 1, max_concurrency].min

ee/spec/lib/gitlab/sidekiq_cluster_spec.rb

@@ -78,12 +78,23 @@ describe Gitlab::SidekiqCluster do
   end
 
   describe '.start_sidekiq' do
+    let(:env) { { "ENABLE_SIDEKIQ_CLUSTER" => "1" } }
+
     it 'starts a Sidekiq process' do
       allow(Process).to receive(:spawn).and_return(1)
 
       expect(described_class).to receive(:wait_async).with(1)
       expect(described_class.start_sidekiq(%w(foo), :production)).to eq(1)
     end
+
+    it 'handles duplicate queue names' do
+      allow(Process).to receive(:spawn)
+                    .with(env, "bundle", "exec", "sidekiq", "-c 5", "-eproduction", "-gqueues: foo (2), bar, baz", anything, "-qfoo,2", "-qbar,1", "-qbaz,1", anything)
+                    .and_return(1)
+
+      expect(described_class).to receive(:wait_async).with(1)
+      expect(described_class.start_sidekiq(%w(foo foo bar baz), :production)).to eq(1)
+    end
   end
 
   describe '.wait_async' do