SylvaUnitsRelease deadlock / too early deletion of source

I have observed the following in a dev environment:

• SUR waiting for flux-system to be ready
• flux-system can't reconcile because depends on root-dependency-xxx
• root-dependency-xxx can't reconcile because it is using a GitRepository source that does not exist

The underlying cause is the fact that the sylva-units-operator deletes the Flux source very early.

A solution we discussed with @stoub and @feleouet is to have the sylva-units-operator prune the unused sources (and also the ConfigMaps/Secrets) only after a full sylva-units reconciliation (ie. when the sylva-units-status Kustomization is ready)