[Feature Request/Question] Controller watch namespaces based on labels (and event sources)

Description

Based on the documentation, the controller is able to dynamically adjust the watched namespaces based on explicit namespace names (often provided through a config map or similar). A convenient extension to this would be able to watch namespaces based on the labels/annotations for a given namespace. I would be helpful if this was built into the machinery of the controller itself, so it could be controlled by some high level configuration

Motivation

Sometimes the creation of new namespaces that need to interact (be watched by) with the operator are done through workflows outside of the purview of the "operator admin". Currently, in order to ensure coverage of all namespaces, either (1) both workflows need to interact and inform the operator deployment when namespaces are added, or (2) the operator simply needs to watch all namespaces. This is where a third option, of only coordinating the appropriate labels would be beneficial

(Somewhat) Related Projects

https://github.com/kubernetes-sigs/hierarchical-namespaces/blob/master/docs/user-guide/concepts.md

Workarounds considered

Use the Kubernetes client itself to query for namespaces upon controller start, periodically poll for changes. Similarly, try to use some form of an Informer to get the same information

まず、controller に既に存在する明示的な namespace 設定と event-source の処理を特定し、次に issue で言及されている Kubernetes client と informer のアプローチを確認します。label と annotation の選択、高レベルの設定、マッチする namespace が作成されたときの動作を明確にします。完了の条件は、workflow の調整やすべての namespace の監視を必要とせずに、controller が選択された namespace を監視することです。