[nn] Add allow_duplicate option for named_modules (#54812)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54812
Needed for quantization since different attribute might refer to the same module instance
Test Plan: Imported from OSS
Reviewed By: vkuzo
Differential Revision: D27408376
fbshipit-source-id: cada85c4a1772d3dd9502c3f6f9a56d690d527e7
