docs: Upgrade Filters documentation to use php8 attributes instead of annotations

[ES-Six]

This PR is intended to enhance the Filter documentation by converting Doctrine annotations to PHP8 attributes since doctrine now supports well the PHP8 attributes:

Here is the list of modifications:

• Every doctrine annotations in the examples have been replaced by doctrine attributes (as in the latest doctrine version, attribute usage is now enabled by default).
• Entity properties typing is now enforced.
• The Doctrine ORM Filter example (UserFilter.php) shows how to create and use a custom attribute instead of how to create a custom annotation.

[dunglas]

Good job!

[ES-Six]

All requested changes have been taken into account.

[dunglas]

Thanks!!