[SPARK-52836] Fix sparkapp.sh to let Spark driver determine pod memory

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

This PR aims to fix the benchmark script `sparkapp.sh` to let Spark Driver determine pod request memory.

### Why are the changes needed?

Apache Spark driver has `spark.driver.memory` is 1g by default and adds overhead when it creates pod. So, we had better use Spark's built-in logic.

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

No, this is a benchmark script change.

### How was this patch tested?

Manual run since the benchmark script is irrelevant to the CI.

```
$ cd tests/benchmark

# The default value is 1k. But, we need to use small value on laptop.
$ ./sparkapps.sh 50
CLEAN UP NAMESPACE FOR BENCHMARK
START BENCHMARK WITH 50 JOBS
FINISHED 50 JOBS IN 52 SECONDS.
DELETED 50 JOBS IN 16 SECONDS.
```

```
# While running the benchmark, we can check the memory.
$ kubectl get pod -l spark-role=driver -oyaml | grep memory | sort | uniq -c
 100           memory: 256Mi
```

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

No.

Closes #289 from dongjoon-hyun/SPARK-52836.

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

Author: dongjoon-hyun

tests/benchmark/sparkapps.sh

@@ -38,8 +38,9 @@ spec:
   jars: "local:///opt/spark/examples/jars/spark-examples.jar"
   driverArgs: ["0"]
   sparkConf:
+    spark.driver.memory: "256m"
+    spark.driver.memoryOverhead: "0m"
     spark.kubernetes.driver.request.cores: "100m"
-    spark.kubernetes.driver.request.memory: "100Mi"
     spark.kubernetes.driver.master: "local[1]"
     spark.kubernetes.authenticate.driver.serviceAccountName: "spark"
     spark.kubernetes.container.image: "apache/spark:4.0.0-java21-scala"