[quant][graphmode] Rename backend_config_dict folder to backend (#69882)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69882
att
Test Plan:
```
python test/fx2trt/test_quant_trt.py
```
Imported from OSS
Reviewed By: supriyar
Differential Revision: D33081761
fbshipit-source-id: c3178eec5798ac8587be09a963944b570c73e8ea
