[quant] update fused_obs_fake_quant op to accept output_fake_quant argument (#65621)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65621
Add a new attribute to the FusedMovingAvgObsFakeQuantize that controls if the Fake Quant operation should be applied at the output of a particular layer. The motivation is to give the users additional control to control the numerics of the fake_quant operators during training. It defaults to always fake quant the output (True).
Note: We will still observer the tensors as before (only the fake_quant operation is controlled using this flag)
For example
```
input model
x -> fc1 -> fc2 -> non_quantizable_op -> fc3
After fake_quant
x -> fake_quant(x) -> fc1 -> fake_quant(fc1) -> fc2 -> fake_quant(fc2) -> non_quantizable_op -> fake_quant() -> fc3 -> fake_quantize(fc3)
With output_fake_quant disabled at the output of fc2 and fc3 (since their outputs are non-quantizable)
x -> fake_quant(x) -> fc1 -> fake_quant(fc1) -> fc2 -> non_quantizable_op -> fake_quant() -> fc3
```
Test Plan: ./buck-out/gen/caffe2/test/quantization_fx\#binary.par -r test_disable_output_fake_quant
Reviewed By: jerryzh168
Differential Revision: D31174526
fbshipit-source-id: bffe776216d041fb09133a6fb09bfc2c0bb46b89
