### What changes were proposed in this pull request?
in `spark-daemon.sh`, `spark_rotate_log()` accepts `$2` as a custom setting for the number of maximum rotate log files, but this part of code is actually never used.
This PR adds `SPARK_LOG_MAX_FILES` environment variable to represent the maximum log files of Spark daemons can rotate to.
### Why are the changes needed?
the logs files that all spark daemons are hardcoded as 5, but it supposed to be configurable
### Does this PR introduce _any_ user-facing change?
yes, SPARK_LOG_MAX_FILES is added to represent the maximum log files of Spark daemons can rotate to.
### How was this patch tested?
verify locally for the added shell script:
```shell
kentyaohulk ~ SPARK_LOG_MAX_FILES=1 sh test.sh
1
kentyaohulk ~ SPARK_LOG_MAX_FILES=a sh test.sh
Error: SPARK_LOG_MAX_FILES must be a postive number
✘ kentyaohulk ~ SPARK_LOG_MAX_FILES=b sh test.sh
Error: SPARK_LOG_MAX_FILES must be a postive number
✘ kentyaohulk ~ SPARK_LOG_MAX_FILES=-1 sh test.sh
Error: SPARK_LOG_MAX_FILES must be a postive number
✘ kentyaohulk ~ sh test.sh
5
✘ kentyaohulk ~ cat test.sh
#!/bin/bash
if [[ -z ${SPARK_LOG_MAX_FILES} ]] ; then
num=5
elif [[ ${SPARK_LOG_MAX_FILES} -gt 0 ]]; then
num=${SPARK_LOG_MAX_FILES}
else
echo "Error: SPARK_LOG_MAX_FILES must be a postive number"
exit -1
fi
```
Closes#28580 from yaooqinn/SPARK-31759.
Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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