sylva-units-operator pre-upgrade Kustomizations dead lock when root-dependency not Ready

This tracks the problem initially discussed in sylva-projects/sylva-elements/sylva-units-operator!575 (comment 3359114636)

When the root-dependency is not ready, then we can have a deadlock:

• s-u-o not updating the sylva-units HelmRelease until pre-update Kustomization are ready
• pre-update Kustomizations can't become ready because they dependsOn root-dependency-
• no deletion of root-dependency-<n> and replacement by root-dependency-<n+1> happens before the sylva-units HelmRelease is updated