Use env vars to trigger hooks

I tried this syntax while creating a hook :

sylius_twig_hooks:
    hooks:
        'sylius_shop.base.header.top_bar':
            my_hook:
                template: '/shop/my_hook.html.twig'
                priority: 0
                enabled: '%env(bool:ENABLE_MY_HOOK)%'

The hook is always enabled, even if the env var ENABLE_MY_HOOK is false.

I tried also to define a parameter like this

parameters:
    app.enable_my_hook: '%env(bool:ENABLE_MY_HOOK)%'

And used it in the hook declaration :

sylius_twig_hooks:
    hooks:
        'sylius_shop.base.header.top_bar':
            my_hook:
                template: '/shop/my_hook.html.twig'
                priority: 0
                enabled: '%app.enable_my_hook%'

This feature flag worked when we used Sylius UI twig events in Sylius 1.x

Reproduce the hook configuration from the issue with ENABLE_MY_HOOK set to false, then inspect the hook configuration handling to see why the enabled value is ignored. Confirm the behavior with both false and true environment values; done means the hook is disabled or enabled accordingly.