[SPARK-53493] Add pi-preview.yaml example

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

This PR aims to add `pi-preview.yaml` for Apache Spark 4.1.0-preview1 (and future preview releases).

### Why are the changes needed?

To give an example with new latest Apache Spark 4.1.0 previews.

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

No. This is a new example.

### How was this patch tested?

Since this is an example, I tested manually.

```
$ k get sparkapp
NAME         CURRENT STATE      AGE
pi-preview   ResourceReleased   6m9s

$ k get sparkapp -oyaml | yq '.items[0].spec.sparkConf."spark.kubernetes.container.image"'
apache/spark:4.1.0-preview1-java21-scala
```

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

Manual.

Closes apache#308 from dongjoon-hyun/SPARK-53493.

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

Author: dongjoon-hyun

examples/pi-preview.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-preview
+spec:
+  mainClass: "org.apache.spark.examples.SparkPi"
+  jars: "local:///opt/spark/examples/jars/spark-examples.jar"
+  sparkConf:
+    spark.dynamicAllocation.enabled: "true"
+    spark.dynamicAllocation.shuffleTracking.enabled: "true"
+    spark.dynamicAllocation.maxExecutors: "3"
+    spark.kubernetes.authenticate.driver.serviceAccountName: "spark"
+    spark.kubernetes.container.image: "apache/spark:4.1.0-preview1-java21-scala"
+  applicationTolerations:
+    resourceRetainPolicy: OnFailure
+  runtimeVersions:
+    sparkVersion: "4.1.0-preview1"