Use autoload instead of relative require

Author: dhh

app/controllers/concerns/importmap/freshness.rb renamed to app/controllers/importmap/freshness.rb

@@ -11,7 +11,7 @@ class Engine < ::Rails::Engine
     config.importmap.cache_sweepers = []
     config.importmap.rescuable_asset_errors = []
 
-    config.autoload_once_paths = %W( #{root}/app/helpers )
+    config.autoload_once_paths = %W( #{root}/app/helpers #{root}/app/controllers )
 
     initializer "importmap" do |app|
       app.importmap = Importmap::Map.new
@@ -50,7 +50,6 @@ class Engine < ::Rails::Engine
 
     initializer "importmap.concerns" do
       ActiveSupport.on_load(:action_controller_base) do
-        require_relative "../../app/controllers/concerns/importmap/freshness"
         extend Importmap::Freshness
       end
     end