[GoodFirst] fix `--cluster-namespace` misleading description

[RainbowMango]

Task description: The description of --cluster-namespace for join command is misleading as the namespace not used to store Cluster objects but the secrets.

# kubectl-karmada join --help 
...
Flags:
...
      --cluster-namespace string    Namespace in the control plane where member cluster are stored. (default "karmada-cluster")

Solution: An alternative is:

diff --git a/pkg/karmadactl/join.go b/pkg/karmadactl/join.go
index acdb3137..937c21c8 100644
--- a/pkg/karmadactl/join.go
+++ b/pkg/karmadactl/join.go
@@ -136,7 +136,7 @@ func (j *CommandJoinOption) Validate() error {
 func (j *CommandJoinOption) AddFlags(flags *pflag.FlagSet) {
        j.GlobalCommandOptions.AddFlags(flags)

-       flags.StringVar(&j.ClusterNamespace, "cluster-namespace", options.DefaultKarmadaClusterNamespace, "Namespace in the control plane where member cluster are stored.")
+       flags.StringVar(&j.ClusterNamespace, "cluster-namespace", options.DefaultKarmadaClusterNamespace, "Namespace in the control plane where member cluster secrets are stored.")

        flags.StringVar(&j.ClusterContext, "cluster-context", "",
                "Context name of cluster in kubeconfig. Only works when there are multiple contexts in the kubeconfig.")
diff --git a/pkg/karmadactl/options/global.go b/pkg/karmadactl/options/global.go
index b1d8902b..6eeb0dca 100644
--- a/pkg/karmadactl/options/global.go
+++ b/pkg/karmadactl/options/global.go
@@ -6,8 +6,7 @@ import (
        "github.com/spf13/pflag"
 )

-// DefaultKarmadaClusterNamespace defines the default namespace where the member cluster objects are stored.
-// The secret owns by cluster objects will be stored in the namespace too.
+// DefaultKarmadaClusterNamespace defines the default namespace where the member cluster secrets are stored.
 const DefaultKarmadaClusterNamespace = "karmada-cluster"

 // DefaultKarmadactlCommandDuration defines the default timeout for karmadactl execute

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[liangyongzhenya]

/assign

[RainbowMango]

Thanks @liangyongzhenya .