[quant][graphmode][fx] Support dynamic quantization without calibration (#43892)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43892
Run weight observer in the convert function, so user do not need to run calibration
Test Plan: Imported from OSS
Reviewed By: vkuzo
Differential Revision: D23429758
fbshipit-source-id: 5bc222e3b731789ff7a86463c449690a58dffb7b
