Precedence between NS labels/annotations propagation should be documented

[erikgb]

What

We are performing a POC of Accurate, and one of our goals is to allow end-users to set selected NS labels/annotations. This seems to work very well, but I could not find the precedence between labelKeys/subNamespaceLabelKeys and annotationKeys/subNamespaceAnnotationKeys documented anywhere. Looking at the code this looks as expected and I have also verified this in our cluster:

https://github.com/cybozu-go/accurate/blob/1cc371dd8d5c1951aa9131c1b382841628a474c9/controllers/namespace_controller.go#L89-L125

But I still think the precedence should be clearly documented (and tested) as a commitment to the current behavior.

How

• Document that SubNamespace annotations/labels will take precedence over any labels/annotations propagated from parent-NS to sub-NS.
• Add tests for this behavior (if not already exists)

Checklist

• [ ] Finish implementation of the issue
• [ ] Test all functions
• [ ] Have enough logs to trace activities
• [ ] Notify developers of necessary actions