sylius.resource_controller.flash_helper has a dependency on a non-existent parameter "locale" - fix

if you have the such error:

The service "sylius.resource_controller.flash_helper" has a dependency on a non-existent parameter "locale". Did you mean one of these: "kernel.default_locale", "stof_doctrine_extensions.default_locale"?

It means you do not have an locale service parameter. To fix this, add this to the beginning of your project config/services.yaml file:

# This file is the entry point to configure your own services.
# Files in the packages/ subdirectory configure your dependencies.

# Put parameters here that don't need to change on each machine where the app is deployed
# https://symfony.com/doc/current/best_practices/configuration.html#application-related-configuration
parameters:
    locale: en