Namespace filter

[fraborg]

The filter on namespace at the moment is very simple: we only use a namespacePrefix argument which allows to run the reconcile method only on LabInstances in the namespaces with that prefix.
It would be nice to have a more generic whitelist, for example something similar to matchLabels used by kubernetes.
@palexster is working on this in #149

[frisso]

@fraborg Can you please add some more details? In your opinion, how the filter should work?

[palexster]

The previous namespace filter is now superseded by a whitelist selector. Each instance of an operator will handle only the instances of namespaces with specific labels (e.g.; production=true). This would allow to have multiple operator running on the cluster without incurring in cross-talk issues.