Documented the console environment variables

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #4162
this is wrong. The console file has a special handling for the prod env, forcing it to be in no-debug mode: https://github.com/symfony/symfony-standard/blob/20516f547e3282a1b3aeec2a284efd311aa9f5a4/app/console#L19
Use ``--env=test`` instead for this case