[SPARK-23449][K8S] Preserve extraJavaOptions ordering

For some JVM options, like `-XX:+UnlockExperimentalVMOptions` ordering is necessary.

## What changes were proposed in this pull request?

Keep original `extraJavaOptions` ordering, when passing them through environment variables inside the Docker container.

## How was this patch tested?

Ran base branch a couple of times and checked startup command in logs. Ordering differed every time. Added sorting, ordering was consistent to what user had in `extraJavaOptions`.

Author: Andrew Korzhuev <korzhuev@andrusha.me>

Closes #20628 from andrusha/patch-2.

resource-managers/kubernetes/docker/src/main/dockerfiles/spark/entrypoint.sh

@@ -41,7 +41,7 @@ fi
 shift 1
 
 SPARK_CLASSPATH="$SPARK_CLASSPATH:${SPARK_HOME}/jars/*"
-env | grep SPARK_JAVA_OPT_ | sed 's/[^=]*=\(.*\)/\1/g' > /tmp/java_opts.txt
+env | grep SPARK_JAVA_OPT_ | sort -t_ -k4 -n | sed 's/[^=]*=\(.*\)/\1/g' > /tmp/java_opts.txt
 readarray -t SPARK_JAVA_OPTS < /tmp/java_opts.txt
 if [ -n "$SPARK_MOUNTED_CLASSPATH" ]; then
   SPARK_CLASSPATH="$SPARK_CLASSPATH:$SPARK_MOUNTED_CLASSPATH"