Handle ioutil deprecations (#53526)

* replace ioutil.ReadFile -> os.ReadFile

* replace ioutil.ReadAll -> io.ReadAll

* replace ioutil.TempFile -> os.CreateTemp

* replace ioutil.NopCloser -> io.NopCloser

* replace ioutil.WriteFile -> os.WriteFile

* replace ioutil.TempDir -> os.MkdirTemp

* replace ioutil.Discard -> io.Discard

pkg/build/plugins/download.go

@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
@@ -54,7 +53,7 @@ func Download(ctx context.Context, grafanaDir string, p syncutil.WorkerPool) err
 	var m pluginsManifest
 	manifestPath := filepath.Join(grafanaDir, "plugins-bundled", "external.json")
 	//nolint:gosec
-	manifestB, err := ioutil.ReadFile(manifestPath)
+	manifestB, err := os.ReadFile(manifestPath)
 	if err != nil {
 		return fmt.Errorf("failed to open plugins manifest %q: %w", manifestPath, err)
 	}

pkg/build/plugins/manifest.go

@@ -7,7 +7,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
@@ -105,7 +104,7 @@ func BuildManifest(ctx context.Context, dpath string, signingAdmin bool) error {
 		}
 	}()
 	if resp.StatusCode != 200 {
-		msg, err := ioutil.ReadAll(resp.Body)
+		msg, err := io.ReadAll(resp.Body)
 		if err != nil {
 			log.Printf("Failed to read response body: %s", err)
 			msg = []byte("")