allow enabling kubelet serving certificate rotation via flag

cmd/kubelet/app/options/options.go

@@ -489,6 +489,7 @@ func AddKubeletConfigFlags(mainfs *pflag.FlagSet, c *kubeletconfig.KubeletConfig
 		"If --tls-cert-file and --tls-private-key-file are not provided, a self-signed certificate and key "+
 		"are generated for the public address and saved to the directory passed to --cert-dir.")
 	fs.StringVar(&c.TLSPrivateKeyFile, "tls-private-key-file", c.TLSPrivateKeyFile, "File containing x509 private key matching --tls-cert-file.")
+	fs.BoolVar(&c.ServerTLSBootstrap, "rotate-server-certificates", c.ServerTLSBootstrap, "<Warning: alpha feature> Auto request and rotate the kubelet serving certificates by requesting new certificates from the kube-apiserver when the certificate expiration approaches. Requires the RotateKubeletServerCertificate feature gate to be enabled.")
 
 	tlsCipherPossibleValues := flag.TLSCipherPossibleValues()
 	fs.StringSliceVar(&c.TLSCipherSuites, "tls-cipher-suites", c.TLSCipherSuites,