add optional dependencies to setup.py; add examples for requirements.txt in examples (meta-pytorch#1430)

Summary:
Pull Request resolved: meta-pytorch#1430

we want to introduce (long term) optional deps for rdma, tensor_engine.
short term, we should put deps on exmaples.

This adds to setup.py

Reviewed By: johnwhumphreys, dcci

Differential Revision: D83884709

fbshipit-source-id: 6baf21bec5588c7c4e8cab2beacb77bf8c1ab481

Author: colin2328

setup.py

@@ -158,6 +158,12 @@ def run(self):
     package_dir={"": "python"},
     python_requires=">= 3.10",
     install_requires=reqs.strip().split("\n"),
+    extras_require={
+        "examples": [
+            "bs4",
+            "ipython",
+        ],
+    },
     license="BSD-3-Clause",
     author="Meta",
     author_email="[email protected]",