[doctrine] Documentation about subscribers is outdated

[Nek-]

The documentation about doctrine state things about subscribers but it's not up to date because the situation changed in the doctrine bundle.

Before:

class MyAwesomeSubscriber implements EventSubscriber
{
    // ...
}

# config/services.yaml
services:
    # ...

    App\Doctrine\MyAwesomeSubscriber:
        tags:
            - { name: 'doctrine.event_subscriber' }

After:

class MyAwesomeSubscriber implements EventSubscriberInterface
{
    // ...
}

(and that's all)

Changed since Doctrine Bundle 2.1.0.

[javiereguiluz]

Maxime, thanks for reporting this issue.

For reference: DoctrineBundle 2.1.0 was released in May 2020: https://github.com/doctrine/DoctrineBundle/releases/tag/2.1.0

So, maybe we could assume that people are already using it ... but even if we update code, we should probably add a note for those using an earlier version of the bundle.