[quant] Expose register activation post process hook function to user (#42342)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/42342
Test Plan: Imported from OSS
Reviewed By: raghuramank100
Differential Revision: D22856711
fbshipit-source-id: d6ad080c82b744ae1147a656c321c448ac5e7f10
