[CELEBORN-1802] Fail the celeborn master/worker start if CELEBORN_CON…

…F_DIR is not directory

### What changes were proposed in this pull request?
Fail the celeborn master/worker start if `CELEBORN_CONF_DIR` is not directory. Otherwise, the  process would run into unexpected status.

### Why are the changes needed?
In the  `celeborn-daemon.sh` , if we specify the `--config <conf-dir>` option. It would fail the master/worker start if the `conf-dir` is not a directory,  likes the systemctl `ConditionPathExists=$CELEBORN_CONF_DIR` requirement check.

https://github.com/apache/celeborn/blob/fde6365f68ce8b589bcc639e96476ed618249257/sbin/celeborn-daemon.sh#L35

https://github.com/apache/celeborn/blob/fde6365f68ce8b589bcc639e96476ed618249257/sbin/celeborn-daemon.sh#L53-L62

But before this PR, for the start master/worker scripts, it did not check if the `CELEBORN_CONF_DIR` is dirctory because the scripts did not leverage `--config <conf-dir>` option.

In this PR, we check the final `CELEBORN_CONF_DIR` before start celeborn, so that all the scripts would check if the `CELEBORN_CONF_DIR` is a directory before start.
### Does this PR introduce _any_ user-facing change?
Yes, it would fail the start if  `CELEBORN_CONF_DIR` is not a directory.

### How was this patch tested?

<img width="840" alt="image" src="https://github.com/user-attachments/assets/e670d21b-cb01-4fa6-8a2f-c94dc06cce4a" />

Closes #3030 from turboFei/check_config_dir.

Authored-by: Wang, Fei <[email protected]>
Signed-off-by: mingji <[email protected]>

sbin/celeborn-daemon.sh

@@ -166,6 +166,11 @@ run_command() {
 }
 
 start_celeborn() {
+    if [ ! -d "$CELEBORN_CONF_DIR" ]
+    then
+      echo "ERROR : CELEBORN_CONF_DIR: $CELEBORN_CONF_DIR is not a directory"
+      exit 1
+    fi
     run_command class "$@"
 }