[SPARK-52296] Add spark-role=operator label

### What changes were proposed in this pull request?

This PR aims to add `spark-role=operator` label.

### Why are the changes needed?

Apache Spark uses `spark-role=xxx` label for all resources. We need to label Spark Operator resources (`Deployment`, `ReplicaSet`, `Pod`) in the same way.

**BEFORE**

```bash
$ kubectl get all -l spark-role=operator
No resources found in default namespace.
```

**AFTER**

```bash
$ kubectl get all -l spark-role=operator
NAME                                            READY   STATUS    RESTARTS   AGE
pod/spark-kubernetes-operator-f44746f8b-nx6w9   1/1     Running   0          2m19s

NAME                                        READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/spark-kubernetes-operator   1/1     1            1           2m19s

NAME                                                  DESIRED   CURRENT   READY   AGE
replicaset.apps/spark-kubernetes-operator-f44746f8b   1         1         1       2m19s
```

### Does this PR introduce _any_ user-facing change?

No behavior change.

### How was this patch tested?

Manually check with `kubectl get all -l spark-role=operator`.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes apache#226 from dongjoon-hyun/SPARK-52296.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

build-tools/helm/spark-kubernetes-operator/templates/_helpers.tpl

@@ -54,6 +54,7 @@ app.kubernetes.io/version: {{ .Chart.AppVersion | quote }}
 {{- end }}
 app.kubernetes.io/managed-by: {{ .Release.Service }}
 helm.sh/chart: {{ include "spark-operator.chart" . }}
+spark-role: operator
 {{- end }}
 
 {{/*

build-tools/helm/spark-kubernetes-operator/templates/spark-operator.yaml

@@ -31,6 +31,7 @@ spec:
   template:
     metadata:
       labels:
+        spark-role: operator
         {{- include "spark-operator.deploymentSelectorLabels" . | nindent 8 }}
         {{- if index (.Values.operatorDeployment.operatorPod) "labels" }}
           {{- with .Values.operatorDeployment.operatorPod.labels }}