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

This PR aims to add a new test tag, `decomTestTag`, to K8s Integration Test.

### Why are the changes needed?

Decommission-related tests took over 6 minutes (`363s`). It would be helpful we can run them selectively.
```
[info] - Test basic decommissioning (44 seconds, 51 milliseconds)
[info] - Test basic decommissioning with shuffle cleanup (44 seconds, 450 milliseconds)
[info] - Test decommissioning with dynamic allocation & shuffle cleanups (2 minutes, 43 seconds)
[info] - Test decommissioning timeouts (44 seconds, 389 milliseconds)
[info] - SPARK-37576: Rolling decommissioning (1 minute, 8 seconds)
```

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

No, this is a test-only change.

### How was this patch tested?

Pass the CIs and test manually.
```
$ build/sbt -Psparkr -Pkubernetes -Pkubernetes-integration-tests \
-Dspark.kubernetes.test.deployMode=docker-desktop "kubernetes-integration-tests/test" \
-Dtest.exclude.tags=minikube,local,decom
...
[info] KubernetesSuite:
[info] - Run SparkPi with no resources (12 seconds, 441 milliseconds)
[info] - Run SparkPi with no resources & statefulset allocation (11 seconds, 949 milliseconds)
[info] - Run SparkPi with a very long application name. (11 seconds, 999 milliseconds)
[info] - Use SparkLauncher.NO_RESOURCE (11 seconds, 846 milliseconds)
[info] - Run SparkPi with a master URL without a scheme. (11 seconds, 176 milliseconds)
[info] - Run SparkPi with an argument. (11 seconds, 868 milliseconds)
[info] - Run SparkPi with custom labels, annotations, and environment variables. (11 seconds, 858 milliseconds)
[info] - All pods have the same service account by default (11 seconds, 5 milliseconds)
[info] - Run extraJVMOptions check on driver (5 seconds, 757 milliseconds)
[info] - Verify logging configuration is picked from the provided SPARK_CONF_DIR/log4j2.properties (12 seconds, 467 milliseconds)
[info] - Run SparkPi with env and mount secrets. (21 seconds, 119 milliseconds)
[info] - Run PySpark on simple pi.py example (13 seconds, 129 milliseconds)
[info] - Run PySpark to test a pyfiles example (14 seconds, 937 milliseconds)
[info] - Run PySpark with memory customization (12 seconds, 195 milliseconds)
[info] - Run in client mode. (11 seconds, 343 milliseconds)
[info] - Start pod creation from template (11 seconds, 975 milliseconds)
[info] - SPARK-38398: Schedule pod creation from template (11 seconds, 901 milliseconds)
[info] - Run SparkR on simple dataframe.R example (14 seconds, 305 milliseconds)
...
```

Closes #37755 from dongjoon-hyun/SPARK-40304.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit fd0498f81df72c196f19a5b26053660f6f3f4d70)
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>