Show full dependency graphs between parent/child namespaces

[Ben8t]

Feature description

While in a parent namespace, users can't see flows from child namespaces (with deps.). It's already possible at a flow level:

https://jam.dev/c/658b4149-069d-48cf-8d47-bb3ce5d7c200

[MilosPaunovic]

If it's similar to #10638, I'd say it's a backend endpoint that needs tweaking, but maybe @loicmathieu could weight in here, as he worked on the mention issue.