[quant][graphmode] Clean up and add more logging (#40196)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40196
- separate passes in insert observers to make it more robust
- added print for quantization type
- added more logging for insert observers
Test Plan: Imported from OSS
Differential Revision: D22106545
fbshipit-source-id: 6d8d722e33c1259b1a6a501853c801c275dbfcff
