quant: nice error message on convtranspose with per-channel weight (#49899)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49899
Per channel weights observer in conv transpose is not supported yet. Adding an
error message which fails instantly instead of making the user wait until after
calibration/training finishes.
Test Plan:
```
python test/test_quantization.py TestPostTrainingStatic.test_convtranspose_per_channel_fails_early
python test/test_quantization.py TestQuantizeFx.test_convtranspose_per_channel_fails_early
```
Imported from OSS
Reviewed By: jerryzh168
Differential Revision: D25717151
fbshipit-source-id: 093e5979030ec185e3e0d56c45d7ce7338bf94b6
