[Workflow] Transition blockers support

[xabbuh]

Transition blockers allow to fetch the reason why applying a transition was blocked (see symfony/symfony#26076).

[noniagriconomie]

there is https://symfony.com/doc/master/workflow/usage.html#transition-blockers
is this issue still relevant?

[xabbuh]

Thank you for checking. Let's close here then as this seems to be solved.