[pruning] Move pruning directory into experimental folder (#60395)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60395
Experimental folder so other developers know this is work in progress
Test Plan:
`buck test mode/dev-nosan //caffe2/test:ao -- TestBasePruner`
https://pxl.cl/1KGJD
Reviewed By: z-a-f
Differential Revision: D29272319
fbshipit-source-id: 93eeeceba0376753efc9a5bb69a155278ceb2fca
