[validation/translations] Add `TranslatableMessage` class to doc

[cavasinf]

Can we add a paragraph in https://github.com/symfony/symfony-docs/blob/6.4/validation/translations.rst about how to translate with TranslatableMessage since it is out from Symfony 6.2 (blog)

Like so:

use Symfony\Component\Translation\TranslatableMessage;
use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;

#[Assert\Callback]
public function validate(ExecutionContextInterface $context, mixed $payload): void
{
    $context->buildViolation(new TranslatableMessage('author.name.not_blank', [], 'validators'))
            ->atPath('name')
            ->addViolation()
    ;
}

[alexandre-daubois]

I think that's a good idea, would you like to provide a PR?

[cavasinf]

First time writing in rst.. but I tried.
Can you check it @alexandre-daubois and tell what need to be changed?

Also, how do you check the final look? With references/code block/... (I'm a Markdown guy)

[alexandre-daubois]

I made a feedback 🙂

If you want to have a look at the "final" look, you can follow steps of the README to build the doc locally: https://github.com/symfony/symfony-docs#build-documentation-locally