[quant][graphmode][fx] Add fbgemm backend_config_dict (#64288)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64288
This is just to setup the file structure and unblock experimentation.
The format for backend_config_dict will change in the future
Test Plan:
python test/test_quantization.py TestQuantizeFx
python test/test_quantization.py TestQuantizeFxOps
Imported from OSS
Reviewed By: zou3519
Differential Revision: D30699457
fbshipit-source-id: 28211a4def05d34757850c045a36e311f54760fe
