[SPARK-53910] Add StatefulSet-based SparkApp example

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to add StatefulSet-based SparkApp example.

Why are the changes needed?

To provide a StatefulSet example with spark.kubernetes.allocation.pods.allocator=statefulset.

Note that this requires the following is a part of v0.6.0.

• [SPARK-53909] Fix RBAC to allow Spark driver to create StatefulSet #389

Does this PR introduce any user-facing change?

No, this is a new example.

How was this patch tested?

Manual review.

$ kubectl apply -f examples/pi-statefulset.yaml
sparkapplication.spark.apache.org/pi-statefulset created

$ kubectl get sparkapp
NAME             CURRENT STATE    AGE
pi-statefulset   RunningHealthy   5s

$ kubectl get pod
NAME                                        READY   STATUS    RESTARTS   AGE
pi-statefulset-0-driver                     1/1     Running   0          7s
spark-kubernetes-operator-cdb4b547d-5bhfm   1/1     Running   0          80s
spark-s-pi-statefulset-0-0-0                1/1     Running   0          5s
spark-s-pi-statefulset-0-0-1                1/1     Running   0          5s
spark-s-pi-statefulset-0-0-2                1/1     Running   0          5s

$ kubectl get sparkapp
NAME             CURRENT STATE      AGE
pi-statefulset   ResourceReleased   48s

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

No.

[dongjoon-hyun]

Thank you, @viirya . Merged to main.