[DDP] Save bucket size limits (#62229)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62229
First of a stack of diffs to save and log the bucket size limits to help debug/discover discrepancies and analyze impact of bucket size tuning
ghstack-source-id: 134475835
Test Plan: CI
Reviewed By: SciPioneer
Differential Revision: D29918629
fbshipit-source-id: b9b3f9a5658340a4c7fd72874c2254664e3c52e9
