feat(frankenphp-symfony): add kernel reboot strategy

[phramz]

I was facing weird side effects regarding PHP sessions and Doctrine ORM running Symfony 6.x and 7.x applications in FrankenPHP worker-mode.

Rebooting the kernel between requests fixed it.

I had this kind of issues back than using Roadrunner as well, so the reboot strategy implementation is inspired by https://github.com/Baldinof/roadrunner-bundle.

Though I guess an on_exception strategy does not make to much sense on a runtime layer (since FrankenPHP will kill the worker if an exception is not handled), it's just 'never' and 'always' for now.