[SPARK-53852] Add spark.kubernetes.driver.pod.excludedFeatureSteps usage example

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

This PR aims to add `spark.kubernetes.driver.pod.excludedFeatureSteps` usage example.

### Why are the changes needed?

Since `Apache Spark K8s Operator v0.6.0`, we can use new features from `Apache Spark 4.1.0-preview2`.
- apache#364

For example, `spark.kubernetes.driver.pod.excludedFeatureSteps` allows us to skip the specific feature steps. If we set the following, we can skip `KerberosConfDriverFeatureStep` which fails always on Java 25 environment currently.

- apache/spark#51522

```
spark.kubernetes.driver.pod.excludedFeatureSteps: "org.apache.spark.deploy.k8s.features.KerberosConfDriverFeatureStep"
```

**BEFORE**

```
25/10/09 04:22:23 INFO pi-preview default o.a.s.i.Logging You have not specified a krb5.conf file locally or via a ConfigMap. Make sure that you have the krb5.conf locally on the driver image.
WARNING: A restricted method in java.lang.System has been called
WARNING: java.lang.System::loadLibrary has been called by org.apache.hadoop.util.NativeCodeLoader in an unnamed module (file:/opt/spark-operator/operator/spark-kubernetes-operator.jar)
WARNING: Use --enable-native-access=ALL-UNNAMED to avoid a warning for callers in this module
WARNING: Restricted methods will be blocked in a future release unless native access is enabled

25/10/09 04:22:23 WARN pi-preview default o.a.h.u.NativeCodeLoader Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
25/10/09 04:22:23 WARN pi-preview default o.a.s.i.Logging Fail to get credentials
java.lang.UnsupportedOperationException: getSubject is not supported
	at java.base/javax.security.auth.Subject.getSubject(Subject.java:277)
	at org.apache.hadoop.security.UserGroupInformation.getCurrentUser(UserGroupInformation.java:588)
	at org.apache.spark.deploy.k8s.features.KerberosConfDriverFeatureStep.liftedTree1$1(KerberosConfDriverFeatureStep.scala:95)
```

**AFTER**

```
25/10/09 04:20:34 INFO pi-preview default o.a.s.i.Logging You have not specified a krb5.conf file locally or via a ConfigMap. Make sure that you have the krb5.conf locally on the driver image.
```

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

No. This is an example update.

### How was this patch tested?

Manual review.

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

No.

Closes apache#379 from dongjoon-hyun/SPARK-53852.

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

Author: dongjoon-hyun

examples/pi-preview.yaml

@@ -25,6 +25,7 @@ spec:
     spark.dynamicAllocation.maxExecutors: "3"
     spark.kubernetes.authenticate.driver.serviceAccountName: "spark"
     spark.kubernetes.container.image: "apache/spark:4.1.0-preview2-java21-scala"
+    spark.kubernetes.driver.pod.excludedFeatureSteps: "org.apache.spark.deploy.k8s.features.KerberosConfDriverFeatureStep"
   applicationTolerations:
     resourceRetainPolicy: OnFailure
   runtimeVersions:

examples/pi.yaml

@@ -25,6 +25,7 @@ spec:
     spark.dynamicAllocation.maxExecutors: "3"
     spark.kubernetes.authenticate.driver.serviceAccountName: "spark"
     spark.kubernetes.container.image: "apache/spark:4.0.1"
+    spark.kubernetes.driver.pod.excludedFeatureSteps: "org.apache.spark.deploy.k8s.features.KerberosConfDriverFeatureStep"
   applicationTolerations:
     resourceRetainPolicy: OnFailure
   runtimeVersions: