Mark OVA generation action as a postprocess task
The action run to generate the ova image isn't currently marked as a postprocess task, so it's being run when the image is still mounted. This has oddly seems to be working in most places, that is until it stopped in a teams use of this recipe resulting in missing boot config files.
Mark this action as a postprocess step to avoid racy behaviour.
For v2024dev1 see !589 (merged)
Edited by Walter Lozano