Pytorch example with alluxiofs

[SibylYang]

An example that uses Alluxiofs to speed up pytorch distributed NLP training with large CSV files.
Formatted the file using black and reorder_python_imports.

[SibylYang]

@lucyge2022 @LuQQiu For your review. Thanks!

[lucyge2022]

so in here, we are already in a child process right?
we can reuse the alluxio_fs instance created per child process when we spawn main() correct?

[SibylYang]

@lucyge2022 Moved alluxio_fs initialization and file preprocessing to the parent process. Add dependencies in the top comment lines.

[lucyge2022]

remove if not needed

[lucyge2022]

LGTM besides comments

[lucyge2022]

@SibylYang also there's some test case failure, the on in CI/lint seems to be bcos of style, can u use pre-commit tool (apt-get install pre-commit) to screen thru the scripts, it will correct the code style for you.
for the CI/Tests , can u make this change to file tests/conftest.py

@@ -93,7 +93,7 @@ def launch_alluxio_dockers(with_etcd=False):
     run_cmd_etcd = (
         "docker run --platform linux/amd64 -d --rm --net=alluxio_network -p 4001:4001 -p 2380:2380 -p 2379:2379 "
         f"-v {TEST_DIR}:/etc/ssl/certs "
-        "--name etcd quay.io/coreos/etcd:latest "
+        "--name etcd quay.io/coreos/etcd:v3.5.13 "

[SibylYang]

@lucyge2022 code updated to address your comments