chore: Replace deprecated io/ioutil functions with recommended alternatives (#9542)

# Which Problems Are Solved

- The `io/ioutil` package was deprecated in Go 1.16.  
  - Reference: https://go.dev/doc/go1.16#ioutil  

# How the Problems Are Solved

- Replaced deprecated functions with their recommended alternatives:  
  - `ioutil.ReadFile` → `os.ReadFile`  
  - `ioutil.ReadAll` → `io.ReadAll`  
  - `ioutil.NopCloser` → `io.NopCloser`

internal/command/project_application_saml_test.go

@@ -3,7 +3,7 @@ package command
 import (
 	"bytes"
 	"context"
-	"io/ioutil"
+	"io"
 	"net/http"
 	"testing"
 
@@ -882,7 +882,7 @@ func newTestClient(httpStatus int, metadata []byte) *http.Client {
 	fn := roundTripperFunc(func(req *http.Request) *http.Response {
 		return &http.Response{
 			StatusCode: httpStatus,
-			Body:       ioutil.NopCloser(bytes.NewBuffer(metadata)),
+			Body:       io.NopCloser(bytes.NewBuffer(metadata)),
 			Header:     make(http.Header), //must be non-nil value
 		}
 	})