[caffe2] Reintroduce Log1p operator (#55073)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55073
Original diff D27422219 (https://github.com/pytorch/pytorch/commit/d92e2520dee8329d5839f5aaf49f51e50a5b8a97) was reverted, reintroducing this op again.
Reviewed By: ChunliF
Differential Revision: D27473735
fbshipit-source-id: 1af0281724e9ada699ebf2045d51f65083daf5b4
