feat: onnx input files

[sid-alluri]

Conversion of input model from .onnx format into .tflite since the transpiler is based on .tflite.

Requirements: onnx2tf

How I tested:

• Downloaded a mnist model in .onnx format into a new example folder
• Followed the same procedure mentioned in https://github.com/ddkang/zkml#converting-your-own-model-and-data
• Code ran successfully and created the required .msgpack files