[Quant][FX] Lower QConvAdd2d for onednn backend (#91153)
**Summary**
Add quantization mappings for QConvAdd2d for int8 inference for onednn backend. The fusion and lowering is supported only in FX mode.
**Test plan**
```
python -m pytest test_quantization.py -k test_fuse_conv_bn_add_relu_onednn
python -m pytest test_quantization.py -k test_fuse_conv_bn_add_relu_by_default
python -m pytest test_quantization.py -k test_fuse_conv_bn_add_relu_lowering
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91153
Approved by: https://github.com/jgong5, https://github.com/jerryzh168
