[SPARK-52647] Fix jvmArgs to support multiple arguments

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

This PR aims to fix `jvmArgs` parameter to support multiple arguments.

https://github.com/apache/spark-kubernetes-operator/blob/a50f4533225d5e2059796426cdfbdf25747dd56a/build-tools/helm/spark-kubernetes-operator/templates/spark-operator.yaml#L104-L105

### Why are the changes needed?

The previous syntax, `"$OPERATOR_JAVA_OPTS"`, cannot handle multiple Java options.

https://github.com/apache/spark-kubernetes-operator/blob/a50f4533225d5e2059796426cdfbdf25747dd56a/build-tools/docker/docker-entrypoint.sh#L29

```
$ cat test.sh
OPERATOR_JAVA_OPTS="-Dfile.encoding=UTF8 -XX:+ExitOnOutOfMemoryError"
exec java "$OPERATOR_JAVA_OPTS" -XX:+PrintFlagsFinal -version

$ sh test.sh | grep ExitOnOutOfMemoryError
     bool ExitOnOutOfMemoryError                   = false                                     {product} {default}
openjdk version "21.0.7" 2025-04-15
OpenJDK Runtime Environment Homebrew (build 21.0.7)
OpenJDK 64-Bit Server VM Homebrew (build 21.0.7, mixed mode, sharing)
```

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

Yes. This is a bug fix.

### How was this patch tested?

Manual review because JVM option check is a little tricky.

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

No.

Closes #267 from dongjoon-hyun/SPARK-52647.

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

Author: dongjoon-hyun

build-tools/docker/docker-entrypoint.sh

@@ -26,7 +26,7 @@ if [ "$1" = "help" ]; then
 elif [ "$1" = "operator" ]; then
   echo "Starting Operator..."
 
-  exec java -cp "./$SPARK_OPERATOR_JAR" "$LOG_CONFIG" "$OPERATOR_JAVA_OPTS" org.apache.spark.k8s.operator.SparkOperator
+  exec java -cp "./$SPARK_OPERATOR_JAR" "$LOG_CONFIG" $OPERATOR_JAVA_OPTS org.apache.spark.k8s.operator.SparkOperator
 fi
 
 args=("${args[@]}")