Use Rails 6.0 defaults and overwrite them

We can remove the `new_framework_defaults_6_0` file by using Rails 6.0
default options and overwriting the ones we haven't enabled.

We're still using the classic autoloader because we still haven't
checked how switching to zeitwerk will affect the way CONSUL
installations customize their code.

And we're using the default queues for Active Storage because we were
already using them and that will be the default option in Rails 6.1.

config/application.rb

@@ -21,7 +21,7 @@ Bundler.require(*Rails.groups)
 
 module Consul
   class Application < Rails::Application
-    config.load_defaults 5.2
+    config.load_defaults 6.0
 
     # Keep belongs_to fields optional by default, because that's the way
     # Rails 4 models worked
@@ -34,6 +34,15 @@ module Consul
     # in any CONSUL installations
     config.active_support.use_authenticated_message_encryption = false
 
+    # Keep using the classic autoloader until we decide how custom classes
+    # should work with zeitwerk
+    config.autoloader = :classic
+
+    # Use the default queue for ActiveStorage like we were doing with Rails 5.2
+    # because it will also be the default in Rails 6.1.
+    config.active_storage.queues.analysis = nil
+    config.active_storage.queues.purge    = nil
+
     # Keep reading existing data in the legislation_annotations ranges column
     config.active_record.yaml_column_permitted_classes = [ActiveSupport::HashWithIndifferentAccess, Symbol]