cubicweb-container #3949517 add migration helper available from container configuration [rejected]

There's a synchronize_container_parent_rdefs function in utils.py. This should be available from the container configuration.

prioritynormal
typeenhancement
done in2.6.0
load0.000
load left0.000
closed by<not specified>
patchAdd a `sync_container_parent` migration command [rejected]