Print SpinApp CRD version on `spin k8s version`

[bacongobbler]

$ spin k8s version

spin k8s version
Plugin Version: unknown
Spin Version  : v2.1.0
Kubernetes Version: v1.27.4+k3s1

# TODO (format TBD)
Spin Operator Version: groupName/version

[VamshiReddy02]

Hi @bacongobbler,
I'd like to work on this issue and have come up with the following solution:

func getSpinOperatorCRDVersion() (string, error) {
		cfg, err := config.GetConfig()
		if err != nil {
			return "", err
		}

		clientset, err := apiextclient.NewForConfig(cfg)
		if err != nil {
			return "", err
		}

		crd, err := clientset.ApiextensionsV1().CustomResourceDefinitions().Get(context.TODO(), "spinapps.core.spinkube.dev", metav1.GetOptions{})
		if err != nil {
			return "", err
		}

		if len(crd.Spec.Versions) > 0 {
			return fmt.Sprintf("%s/%s", crd.Spec.Group, crd.Spec.Versions[0].Name), nil
		}

		return "unknown", nil
	}

Do you think this is a reasonable approach, or would you suggest any improvements?