Add Support for Symfony 5 and 6

[jordisala1991]

Subject

I am targeting this branch, because this is BC break.

Closes #1410

Changelog

### Added
- Add support for Symfony 5 and 6.

[jordisala1991]

Depends on how hard is fixing the: LogoutHandlerInterface, we might do first 5.4 and then 6.0 or in the same PR.

use Symfony\Component\Security\Http\Logout\LogoutHandlerInterface; used in CmsManagerSelector.

[VincentLanglet]

int|string I think.

[jordisala1991]

Im trying to focus only on needed changes for sf 5/6. This will go to a PHPStan up PR.

[jordisala1991]

There is some work to do still.

[jordisala1991]

Here the Pr for dev kit: sonata-project/dev-kit#2121