.github: Add workflow to stale pull requests (#51237)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51237
Stales pull requests at 150 days and then will close them at 180 days
Signed-off-by: Eli Uriegas <eliuriegas@fb.com>
Test Plan: stonks
Reviewed By: yns88
Differential Revision: D26112086
Pulled By: seemethere
fbshipit-source-id: c6b3865aa5cde3415b6dd6622c308895a16e805f
