[SPARK-53910] Add StatefulSet-based SparkApp example

### 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`.
- #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.

Closes #390 from dongjoon-hyun/SPARK-53910.

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

Author: dongjoon-hyun

examples/pi-statefulset.yaml

@@ -0,0 +1,31 @@
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+apiVersion: spark.apache.org/v1
+kind: SparkApplication
+metadata:
+  name: pi-statefulset
+spec:
+  mainClass: "org.apache.spark.examples.SparkPi"
+  driverArgs: ["20000"]
+  jars: "local:///opt/spark/examples/jars/spark-examples.jar"
+  sparkConf:
+    spark.executor.instances: "3"
+    spark.kubernetes.allocation.pods.allocator: "statefulset"
+    spark.kubernetes.authenticate.driver.serviceAccountName: "spark"
+    spark.kubernetes.container.image: "apache/spark:4.0.1"
+  applicationTolerations:
+    resourceRetainPolicy: OnFailure
+  runtimeVersions:
+    sparkVersion: "4.0.1"