Add the capability to dump inventory of related units.

This idea was suggested by @tmmorin

When sylvactl timeouts on some units like cluster-machines-ready, it dumps the inventory of the corresponding kustomization which is not usefull. In this case we would need the inventory of the cluster unit that would be more relevant, but it is not included since the cluster is seen as Ready.

We could use an annotation on these units to instruct sylvactl to also perform the inventory of these related units, even if they are seen as ready.

The annotation could be for example:

sylvactl/dumpInventory: Kustomization/sylva-system/cluster,Kustomization/sylva-system/cluster-bmh