Add ValidatingAdmissionWebhook for Stash CRDs (#299)

* Add ValidatingAdmissionWebhook for Stash CRDs

ref: https://github.com/openshift/kubernetes-namespace-reservation

* Add admission installer

* Update docs

Author: tamalsaha

root.go

@@ -3,16 +3,21 @@ package cmds
 import (
 	"flag"
 	"log"
+	"os"
 	"strings"
 
 	"github.com/appscode/go/log/golog"
 	v "github.com/appscode/go/version"
 	"github.com/appscode/kutil/tools/analytics"
 	"github.com/appscode/stash/client/scheme"
+	"github.com/appscode/stash/pkg/admission/plugin/recovery"
+	"github.com/appscode/stash/pkg/admission/plugin/restic"
 	"github.com/appscode/stash/pkg/util"
 	"github.com/jpillora/go-ogle-analytics"
+	"github.com/openshift/generic-admission-server/pkg/cmd/server"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
+	genericapiserver "k8s.io/apiserver/pkg/server"
 	clientsetscheme "k8s.io/client-go/kubernetes/scheme"
 )
 
@@ -52,5 +57,11 @@ func NewRootCmd() *cobra.Command {
 	rootCmd.AddCommand(NewCmdBackup())
 	rootCmd.AddCommand(NewCmdRecover())
 	rootCmd.AddCommand(NewCmdCheck())
+
+	stopCh := genericapiserver.SetupSignalHandler()
+	cmd := server.NewCommandStartAdmissionServer(os.Stdout, os.Stderr, stopCh, &restic.AdmissionHook{}, &recovery.AdmissionHook{})
+	cmd.Use = "admission-webhook"
+	rootCmd.AddCommand(cmd)
+
 	return rootCmd
 }