Add ObjectStorageQueue concern and test

app/workers/concerns/object_storage_queue.rb

+# Concern for setting Sidekiq settings for the various GitLab ObjectStorage workers.
+module ObjectStorageQueue
+  extend ActiveSupport::Concern
+
+  included do
+    queue_namespace :object_storage
+  end
+end

spec/workers/concerns/object_storage_queue_spec.rb

+require 'spec_helper'
+
+describe ObjectStorageQueue do
+  let(:worker) do
+    Class.new do
+      def self.name
+        'DummyWorker'
+      end
+
+      include ApplicationWorker
+      include ObjectStorageQueue
+    end
+  end
+
+  it 'sets a default object storage queue automatically' do
+    expect(worker.sidekiq_options['queue'])
+      .to eq 'object_storage:dummy'
+  end
+end