Add OIDC auth support in kubectl-etcd plugin (#272)

Subj. Without such import, there is auth error:

```
Error setting up etcd client: error creating Kubernetes client: no Auth Provider found for name "oidc"
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **New Features**
- Introduced commands for managing etcd pods, including status checks,
defragmentation, compaction, alarm management, and member management.
  
- **Bug Fixes**
- Standardized error handling for improved user feedback during command
execution.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: evgkrsk

cmd/kubectl-etcd/main.go

@@ -20,6 +20,7 @@ import (
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
+	_ "k8s.io/client-go/plugin/pkg/client/auth" // Import all auth providers
 	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/client-go/tools/portforward"
 	"k8s.io/client-go/transport/spdy"