Support Convolution2DTransposeBias conversion

[Honry]

I am trying to convert Selfie Segmentation TFLite model to ONNX, but which includes a custom op Convolution2DTransposeBias. So this is a feature request to support conversion of this op in tf2onnx, I suppose this should be supported by ONNX's ConvTranspose.

[hwangdeyu]

The Convolution2DTranspose with Bias term would be suuported when this issues fixed. #1740

[hwangdeyu]

This script result of this issue is changed cause #1741 added the optimize() logic for tf1 keras conversion.
Please consider creating a new issue if there are leftover issues.