### What changes were proposed in this pull request?
`SparkShuffleManager` print warning log for `spark.executor.userClassPathFirst=true` with `ShuffleManager` defined in user jar via `--jar` or `spark.jars`.
### Why are the changes needed?
When `spark.executor.userClassPathFirst` is enabled with ShuffleManager defined in user jar, the `ClassLoader` of `handle` is `ChildFirstURLClassLoader`, which is different from `CelebornShuffleHandle` of which the `ClassLoader` is `AppClassLoader` in `SparkShuffleManager#getWriter/getReader`. The local test log is as follows:
```
./bin/spark-sql --master yarn --deploy-mode client \
--conf spark.celeborn.master.endpoints=localhost:9099 \
--conf spark.executor.userClassPathFirst=true \
--conf spark.jars=/tmp/celeborn-client-spark-3-shaded_2.12-0.5.0-SNAPSHOT.jar \
--conf spark.shuffle.manager=org.apache.spark.shuffle.celeborn.SparkShuffleManager \
--conf spark.shuffle.service.enabled=false
./bin/spark-sql --master yarn --deploy-mode client --jars /tmp/celeborn-client-spark-3-shaded_2.12-0.5.0-SNAPSHOT.jar \
--conf spark.celeborn.master.endpoints=localhost:9099 \
--conf spark.executor.userClassPathFirst=true \
--conf spark.shuffle.manager=org.apache.spark.shuffle.celeborn.SparkShuffleManager \
--conf spark.shuffle.service.enabled=false
```
```
24/04/28 18:03:31 [Executor task launch worker for task 0.0 in stage 5.0 (TID 8)] WARN SparkShuffleManager: [getWriter] handle classloader: org.apache.spark.util.ChildFirstURLClassLoader, CelebornShuffleHandle classloader: sun.misc.Launcher$AppClassLoader
```
It causes that `SparkShuffleManager` fallback to vanilla Spark `SortShuffleManager` for `spark.executor.userClassPathFirst=true` with `ShuffleManager` defined in user jar before https://github.com/apache/spark/pull/43627. After [SPARK-45762](https://issues.apache.org/jira/browse/SPARK-45762), the `ClassLoader` of `handle` and `CelebornShuffleHandle` are both `ChildFirstURLClassLoader`.
```
24/04/28 18:03:31 [Executor task launch worker for task 0.0 in stage 5.0 (TID 8)] WARN SparkShuffleManager: [getWriter] handle classloader: org.apache.spark.util.ChildFirstURLClassLoader, CelebornShuffleHandle classloader: org.apache.spark.util.ChildFirstURLClassLoader
```
Therefore, `SparkShuffleManager` should print warning log to remind for `spark.executor.userClassPathFirst=true` with `ShuffleManager` defined in user jar.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Manual test.
Closes#2482 from SteNicholas/CELEBORN-1402.
Authored-by: SteNicholas <programgeek@163.com>
Signed-off-by: SteNicholas <programgeek@163.com>
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