fix: use kubeconfig file when user specify it (#605)

If user specify `--kubeconfig` when running k8sgpt, it should use the
kubeconfig file to login the corresponding cluster instead of getting auth info via SA.

Closes #604

Signed-off-by: Jian Zhang <jiazha@redhat.com>

pkg/kubernetes/kubernetes.go

@@ -36,14 +36,11 @@ func (c *Client) GetRestClient() rest.Interface {
 
 func NewClient(kubecontext string, kubeconfig string) (*Client, error) {
 	var config *rest.Config
-	config, err := rest.InClusterConfig()
-	if err != nil {
-		loadingRules := clientcmd.NewDefaultClientConfigLoadingRules()
-
-		if kubeconfig != "" {
-			loadingRules.ExplicitPath = kubeconfig
-		}
+	var err error
 
+	if kubeconfig != "" {
+		loadingRules := clientcmd.NewDefaultClientConfigLoadingRules()
+		loadingRules.ExplicitPath = kubeconfig
 		clientConfig := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
 			loadingRules,
 			&clientcmd.ConfigOverrides{
@@ -54,7 +51,13 @@ func NewClient(kubecontext string, kubeconfig string) (*Client, error) {
 		if err != nil {
 			return nil, err
 		}
+	} else {
+		config, err = rest.InClusterConfig()
+		if err != nil {
+			return nil, err
+		}
 	}
+
 	clientSet, err := kubernetes.NewForConfig(config)
 	if err != nil {
 		return nil, err