Defer loading when active record is properly loaded

This is well known issue. We should prefer to code that reference active
record only when it's already lazy loaded.
It can break other gems initializing process

Related:
- rails/rails#46567
- paper-trail-gem/paper_trail@fc6c5f6
(inspiration)
- thoughtbot/factory_bot_rails#432

Fix: DatabaseCleaner#89

lib/database_cleaner-active_record.rb

@@ -1 +1 @@
-require "database_cleaner/active_record"
+require "database_cleaner/active_record/railtie"

lib/database_cleaner/active_record/railtie.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module DatabaseCleaner::ActiveRecord
+  class Railtie < ::Rails::Railtie
+    initializer "database_cleaner-active_record" do
+      ActiveSupport.on_load(:active_record) do
+        require "database_cleaner/active_record"
+      end
+    end
+  end
+end