[Validator] - EmailConstraint reference

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes - https://github.com/symfony/symfony/pull/9140
| Applies to    | master
| Fixed tickets | 

Note
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I'm not sure if this behaviour change should go in a page by itself (like https://github.com/symfony/symfony-docs/blob/2.4/components/dependency_injection/lazy_services.rst) since requires the installation of an external library to work.
I appreciate some guide on this since it's my first doc PR, thanks.