Create a documentation page for `torch.ao.quantization.QConfig` (#66129)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66129
Adds a documentation page for `torch.ao.quantization.QConfig`. It is useful
for this to have a separate page since it shared between Eager and FX graph
mode quantization.
Also, ensures that all important functions and module attributes in this
module have docstrings, so users can discover these without reading the
source code.
Test Plan:
```
cd docs
make html
python -m http.server
// open webpage, inspect it, renders correctly
```
Reviewed By: jerryzh168
Differential Revision: D31447614
Pulled By: vkuzo
fbshipit-source-id: 5d9dd2a4e8647fa17b96cefbaae5299adede619c
