fix(di): refers to the key to be able to override by env

[R2c]

When we try to override the configuration (like for dev/test env) we got this error :

In ContainerBuilder.php line 1381:
                                                                               
  Invalid argument name "0" for service "html_sanitizer.0": the first character must be a letter. 

Symfony documentation explain :

[R2c]

@tgalopin up =)

[tgalopin]

Thanks!