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/monitoring/v1alpha3/handler.go

@@ -21,7 +21,7 @@ package v1alpha3
 import (
 	"context"
 	"errors"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"net/url"
 	"regexp"
@@ -364,7 +364,7 @@ func (h handler) handleGrafanaDashboardImport(req *restful.Request, resp *restfu
 
 			defer r.Body.Close()
 
-			c, err := ioutil.ReadAll(r.Body)
+			c, err := io.ReadAll(r.Body)
 			if err != nil {
 				return nil, err
 			}