[quant][docs] Add more docs for quantization.rst (#75998)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75998
Add more details to user facing docs quantization.rst, which will be displayed in the official quantization doc page: https://pytorch.org/docs/stable/quantization.html
This includes:
* docs for quantization stack (quantized tensor, quantized operator and modules, observer, fake_quantize, QConfig, quantization flow)
* Added support table for quantization mode, quantization flow mode and backend, (also moved around operator support table)
* restructured eager mode and fx mode docs as well
Test Plan:
inspect the doc that's built by github ci
Imported from OSS
Reviewed By: dzdang
Differential Revision: D35739111
fbshipit-source-id: 3762d387479bdd37472cb17d5c49da2f520effbb
(cherry picked from commit db5e6411c52c08dd9c45f841ab86713d36a75d51)
