Avoid loading workers before setting Sidekiq defaults

Not a current bug, but it's possible that Sidekiq workers
are referenced before having a chance to load its defaults.

It means that it could run a worker with a wrong `retry`
default, for instance.

Here we solve that by loading it at the
`config/initializers_before_autoloader`, which is a
initializer that loads before autoloading happens.

config/initializers/sidekiq.rb

 # frozen_string_literal: true
 
-require 'sidekiq/web'
-
 def enable_reliable_fetch?
   return true unless Feature::FlipperFeature.table_exists?
 
@@ -14,21 +12,10 @@ def enable_semi_reliable_fetch_mode?
   Feature.enabled?(:gitlab_sidekiq_enable_semi_reliable_fetcher, default_enabled: true)
 end
 
-# Disable the Sidekiq Rack session since GitLab already has its own session store.
-# CSRF protection still works (https://github.com/mperham/sidekiq/commit/315504e766c4fd88a29b7772169060afc4c40329).
-Sidekiq::Web.set :sessions, false
-
 # Custom Queues configuration
 queues_config_hash = Gitlab::Redis::Queues.params
 queues_config_hash[:namespace] = Gitlab::Redis::Queues::SIDEKIQ_NAMESPACE
 
-# Default is to retry 25 times with exponential backoff. That's too much.
-Sidekiq.default_worker_options = { retry: 3 }
-
-if Rails.env.development?
-  Sidekiq.default_worker_options[:backtrace] = true
-end
-
 enable_json_logs = Gitlab.config.sidekiq.log_format == 'json'
 enable_sidekiq_memory_killer = ENV['SIDEKIQ_MEMORY_KILLER_MAX_RSS'].to_i.nonzero?
 use_sidekiq_daemon_memory_killer = ENV["SIDEKIQ_DAEMON_MEMORY_KILLER"].to_i.nonzero?

config/initializers_before_autoloader/002_sidekiq.rb

+# frozen_string_literal: true
+
+# Preloads Sidekiq configurations that don't require application references.
+#
+# It ensures default settings are loaded before any other file references
+# (directly or indirectly) Sidekiq workers.
+#
+
+require 'sidekiq/web'
+
+# Disable the Sidekiq Rack session since GitLab already has its own session store.
+# CSRF protection still works (https://github.com/mperham/sidekiq/commit/315504e766c4fd88a29b7772169060afc4c40329).
+Sidekiq::Web.set :sessions, false
+
+# Default is to retry 25 times with exponential backoff. That's too much.
+Sidekiq.default_worker_options = { retry: 3 }
+
+if Rails.env.development?
+  Sidekiq.default_worker_options[:backtrace] = true
+end