Add serializer and deserializer for Int8QuantSchemeBlob and Int8QuantParamsBlob (#40661)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40661
Add ser-de to support int8 quantization during online training
Test Plan:
```
buck test caffe2/caffe2/fb/fbgemm:int8_serializer_test
```
Reviewed By: hx89
Differential Revision: D22273292
fbshipit-source-id: 3b1e9c820243acf41044270afce72a262ef92bd4
