Remove use of Redis multi in Sidekiq client

When pushing jobs to Redis, Sidekiq client uses a Redis multi call. For
scheduled jobs, this is actually not needed because we're only executing
one Redis command. For other jobs, the commands don't need to be atomic.

This reduces the work the Redis server needs to do.

Changelog: performance

config/initializers/sidekiq.rb

@@ -114,3 +114,5 @@ Sidekiq.configure_client do |config|
 
   config.client_middleware(&Gitlab::SidekiqMiddleware.client_configurator)
 end
+
+Sidekiq::Client.prepend Gitlab::Patch::SidekiqClient

lib/gitlab/patch/sidekiq_client.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Patch
+    module SidekiqClient
+      private
+
+      # This is a copy of https://github.com/mperham/sidekiq/blob/v6.2.2/lib/sidekiq/client.rb#L187-L194
+      # but using `conn.pipelined` instead of `conn.multi`. The multi call isn't needed here because in
+      # the case of scheduled jobs, only one Redis call is made. For other jobs, we don't really need
+      # the commands to be atomic.
+      def raw_push(payloads)
+        @redis_pool.with do |conn| # rubocop:disable Gitlab/ModuleWithInstanceVariables
+          conn.pipelined do
+            atomic_push(conn, payloads)
+          end
+        end
+        true
+      end
+    end
+  end
+end