improve root-dependency wait checks

This MR does two things on the code handling how the root-dependency unit Job waits for sylva-units Kustomizations to have been updated:

• ensure that it waits for all the Kustomizations, except the ones for the root-dependency (or else, if we hit cases where Kustomizations root-dependency-<n-1> and dependency-<n> exist both at the same time --which I've seen in corner cases-- then the script waits forever on root-dependency- having the label for the Helm release )
• use an annotation instead of a label to store the Helm revision -- this was suggested by @feleouet as a good practive (labels aren't cheap, it's better to use annotations when possible, ie. when we don't use the k=v for a lookup)