Dummy unit generate no resource

What does this MR do and why?

The "mgmt-cluster-ready" units are generating ConfigMaps in the sylva-system namespace instead of their respective namespaces. This occurs because the namespace is hardcoded in the unit definition. When managing multiple workload clusters, deleting one leaves the associated ConfigMap intact, which causes the deletion job for the Sylva unit to enter an infinite loop.

This MR addresses the issue by updating the Sylva unit name dummy to not generate any resource (the resource currently produced is a configmap that had been introduced at some point just because Flux had a bug preventing Kustomizations defining no resource; this bug has since been fixed ).

Closes #1645 (closed)