Introduce new upload way with required reproduction files

[jcwchen]

Description

• New upload way: 6 required files
  • single .onnx file
  • model.py to get the models from torch hub, torchvision, transformers or etc.
  • requirements.txt for required Python dependency version to repro
  • test_data_set_0, which can be obtained from onnxruntime's ort_test_dir_utils.
  • READMD.md for model documentation.
  • LICENSE file.
• Add CI to validate new models
• Add alexnet as an example
• Apply mlagility to verify models
• Update contribute tutorials

Motivation
Currently a lot of existing ONNX models in this repo is hard to repro. Propose a new upload way with required reproduction files.