Quantization docs: add pages for Numeric Suite (Eager and FX) (#66380)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66380
Description:
1. creates doc pages for Eager and FX numeric suites
2. adds a link from main quantization doc to (1)
3. formats docblocks in Eager NS to render well
4. adds example code and docblocks to FX numeric suite
Test Plan:
```
cd docs
make html
python -m http.server
// renders well
```
Reviewed By: jerryzh168
Differential Revision: D31543173
Pulled By: vkuzo
fbshipit-source-id: feb291bcbe92747495f45165f738631fa5cbffbd
