refactor: move from io/ioutil to io and os packages (#5266)

The io/ioutil package has been deprecated as of Go 1.16 [1]. This commit
replaces the existing io/ioutil functions with their new definitions in
io and os packages.

[1]: https://golang.org/doc/go1.16#ioutil
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/kapis/notification/v2beta2/handler.go

@@ -16,7 +16,7 @@
 package v2beta2
 
 import (
-	"io/ioutil"
+	"io"
 
 	"github.com/emicklei/go-restful"
 	"k8s.io/apimachinery/pkg/api/errors"
@@ -131,7 +131,7 @@ func (h *handler) PatchResource(req *restful.Request, resp *restful.Response) {
 		return
 	}
 
-	data, err := ioutil.ReadAll(req.Request.Body)
+	data, err := io.ReadAll(req.Request.Body)
 	if err != nil {
 		api.HandleBadRequest(resp, req, err)
 		return