set skipped-propagating-namespaces for karmada controller manager behavior inconsistent with doc

[wu0407]

What happened:

If set --skipped-propagating-namespaces=xxx for karmada controller manager, and xxx is not kube-*, then kube-system namespace will be sync to member cluster. It inconsistent with doc.

Note: Avoid creating namespaces with the prefix kube- and karmada-, since they are reserved for Kubernetes and Karmada system namespaces. For now, resources under the following namespaces will not be propagated:

namespaces prefix kube-(including but not limited to kube-system, kube-public, kube-node-lease)
karmada-system
karmada-cluster
karmada-es-*

E0808 07:11:30.045105       1 controller.go:329] "Reconciler error" err="resource(kind=Namespace, /kube-system) already exist in cluster test-cluster and the work.karmada.io/conflict-resolution strategy value is empty, karmada will not manage this resource" controller="work" controllerGroup="work.karmada.io" controllerKind="Work" Work="karmada-es-test-cluster/kube-system-9686d6fdd" namespace="karmada-es-test-cluster" name="kube-system-9686d6fdd" reconcileID=79c5ed2b-a183-4a9c-b4c6-d49f1e3d6d1d

What you expected to happen:
not propagating kube-* namespace

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• Karmada version:
• kubectl-karmada or karmadactl version (the result of kubectl-karmada version or karmadactl version):
• Others:

kubectl karmada version: version.Info{GitVersion:"v1.6.1", GitCommit:"fdc7ac62c70b571d091a795cbe9b9fceac5f1c2c", GitTreeState:"clean", BuildDate:"2023-07-06T03:35:37Z", GoVersion:"go1.20.4", Compiler:"gc", Platform:"linux/amd64"}

[wu0407]

#3433

[RainbowMango]

@chaunceyjiang Could you please take a look?

[chaunceyjiang]

/assign

[chaunceyjiang]

If set --skipped-propagating-namespaces=xxx for karmada controller manager, and xxx is not kube-*, then kube-system namespace will be sync to member cluster

This is as expected.

namespaces prefix kube-(including but not limited to kube-system, kube-public, kube-node-lease)

This is the default behavior, which is set as --skipped-propagating-namespaces=kube-.* by default.
If you set it to --skipped-propagating-namespaces=xxx, it means you have modified the default behavior, so kube-system will be synchronized to member clusters.

Later, I will go and modify the document to add more explanations in order to reduce such misunderstandings.

[RainbowMango]

      --skipped-propagating-namespaces strings                                                                                                                                                      
                Comma-separated namespaces that should be skipped from propagating.
                Note: 'karmada-system', 'karmada-cluster' and 'karmada-es-.*' are Karmada reserved namespaces that will always be skipped. (default [kube-.*])

Should we update the usage with more description to avoid misunderstanding?

[chaunceyjiang]

/kind cleanup
/kind-remove bug