Support namespaceLabelSelector field in ClusterAgentConfiguration spec

[kennethredler]

I want the scope of a ClusterAgentConfiguration to apply to the set of Namespaces identified by the label or labels that are applied on the Namespace(s).

I do not want to have to update an explicit list of Namespace names on the ClusterAgentConfiguration resource.

[vranyes]

plus one, this is a great idea - maintaining a comprehensive list of all namespaces that need injection is not ideal - and label selectors are a common Kubernetes pattern