Deprecate KubeletConfiguration flags

This is a follow-up to kubernetes#53833 to deprecate the old flags in favor of the
config file.

cmd/kubelet/app/options/options.go

@@ -420,7 +420,22 @@ func (f *KubeletFlags) AddFlags(fs *pflag.FlagSet) {
 }
 
 // AddKubeletConfigFlags adds flags for a specific kubeletconfig.KubeletConfiguration to the specified FlagSet
-func AddKubeletConfigFlags(fs *pflag.FlagSet, c *kubeletconfig.KubeletConfiguration) {
+func AddKubeletConfigFlags(mainfs *pflag.FlagSet, c *kubeletconfig.KubeletConfiguration) {
+	fs := pflag.NewFlagSet("", pflag.ExitOnError)
+	defer func() {
+		// All KubeletConfiguration flags are now deprecated, and any new flags that point to
+		// KubeletConfiguration fields are deprecated-on-creation. When removing flags at the end
+		// of their deprecation period, be careful to check that they have *actually* been deprecated
+		// members of the KubeletConfiguration for the entire deprecation period:
+		// e.g. if a flag was added after this deprecation function, it may not be at the end
+		// of its lifetime yet, even if the rest are.
+		deprecated := "This parameter should be set via the config file specified by the Kubelet's --config flag. See https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/ for more information."
+		fs.VisitAll(func(f *pflag.Flag) {
+			f.Deprecated = deprecated
+		})
+		mainfs.AddFlagSet(fs)
+	}()
+
 	fs.BoolVar(&c.FailSwapOn, "fail-swap-on", c.FailSwapOn, "Makes the Kubelet fail to start if swap is enabled on the node. ")
 	fs.BoolVar(&c.FailSwapOn, "experimental-fail-swap-on", c.FailSwapOn, "DEPRECATED: please use --fail-swap-on instead.")
 	fs.MarkDeprecated("experimental-fail-swap-on", "This flag is deprecated and will be removed in future releases. please use --fail-swap-on instead.")