Speed up boot time in production

In production mode, eager loading is enabled, and Devise is configured
by default to reload routes before eager loading. However, in
`config/application.rb` we also attempted to reload routes, which added
another 5-10 seconds of delay. In development mode, eager loading is
disabled, so we don't see this extra overhead.

To speed boot times, we only reload the routes if eager loading is
disabled.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/213992

changelogs/unreleased/sh-avoid-extra-route-reload.yml

+---
+title: Speed up boot time in production
+merge_request: 33929
+author:
+type: performance

config/application.rb

@@ -301,7 +301,10 @@ module Gitlab
     end
 
     config.after_initialize do
-      Rails.application.reload_routes!
+      # Devise (see initializers/8_devise.rb) already reloads routes if
+      # eager loading is enabled, so don't do this twice since it's
+      # expensive.
+      Rails.application.reload_routes! unless config.eager_load
 
       project_url_helpers = Module.new do
         extend ActiveSupport::Concern

config/initializers/8_devise.rb

@@ -6,6 +6,11 @@ Devise.setup do |config|
     manager.default_strategies(scope: :user).unshift :two_factor_backupable
   end
 
+  # This is the default. This makes it explicit that Devise loads routes
+  # before eager loading. Disabling this seems to cause an error loading
+  # grape-entity `expose` for some reason.
+  config.reload_routes = true
+
   # ==> Mailer Configuration
   # Configure the class responsible to send e-mails.
   config.mailer = "DeviseMailer"