Pytorch/Brevitas improvement for hls4ml

Created by: Duchstf

Creating an issue here for discussion on Pytorch/Brevitas improvement. I'll create an initial PR based off Pedro's codes soon (probably next week).

I think the main things I want to discuss here are:

1. What kinds of functionality/improvement we need to target in order to make Pytorch/Brevitas support on par with the current Keras/QKeras scheme.

2. I think we should start gather more example models for Pytorch/Brevitas.