Fix retrieval of CRUD controller FQCN for batch action with pretty URLs

[thomas-l]

The batch action failed with pretty URLs.

Fixes https://github.com/EasyCorp/EasyAdminBundle/issues/6723

[thomas-l]

Custom actions must now use the attribute #[AdminAction] to make them work.

The documentation says

Custom actions can define the #[AdminAction]

Which is "must define" in the current case.

I'll transform my PR to cover both cases.