[quant] ao migration of observer and qconfig (#64982)

[quant] ao migration of observer and qconfig (#64982)

Summary:
(Had to recreate this diff so it wasn't dependent on the stack)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/64982

migration of qconfig.py and observer.py to torch/ao/quantization using new test format
ghstack-source-id: 138215256

Test Plan:
buck test mode/opt //caffe2/test:quantization

https://www.internalfb.com/intern/testinfra/testconsole/testrun/8444249354294701/

buck test mode/dev //caffe2/test:quantization -- TestAOMigrationQuantization

https://www.internalfb.com/intern/testinfra/testrun/3940649742829796

Reviewed By: z-a-f

Differential Revision: D30982534

fbshipit-source-id: 48d08969b1984311ceb036eac0877c811cd6add9