New trained model type requires .zip in output folder even though no .zip required for model

[mattdawkins]

Describe the bug
When training a new model type, particularly train_detector_mmdet_convnext_cascade.conf on latest VIAME (v0.20.1), if the output folder does not contain a .zip file, then the pipelines do not show up in the desktop version under the 'Trained' dropdown, despite being successfully trained. Web version untested. The model produces a .py. .pipe, .pth, and .txt files but no .zip on success.

For now, I've had them produce a dummy .zip file so that they show up under the 'Trained' dropdown in Desktop, though the .zip file is just an empty file

I think I'm worried that the same situation might be encountered for other model types, e.g. YOLOs, SVMs, MMDet models which also don't produce .zips, but also untested