replace deprecated ioutil (#2531)

* replace deprecated ioutil
* replace ioutil also in kubectl plugin

pkg/spec/types.go

@@ -4,7 +4,6 @@ import (
 	"database/sql"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"strings"
@@ -210,7 +209,7 @@ func GetOperatorNamespace() string {
 		if namespaceFromEnvironment := os.Getenv("OPERATOR_NAMESPACE"); namespaceFromEnvironment != "" {
 			return namespaceFromEnvironment
 		}
-		operatorNamespaceBytes, err := ioutil.ReadFile(fileWithNamespace)
+		operatorNamespaceBytes, err := os.ReadFile(fileWithNamespace)
 		if err != nil {
 			log.Fatalf("Unable to detect operator namespace from within its pod due to: %v", err)
 		}