[ao][ns] PNP demo for exposing arbitrary model transforms (#90153)
adding way to use arbitrary prepare and convert functions with PNP.
note this is a recreation of https://github.com/pytorch/pytorch/pull/89892 which was reverted due to landing not syncing between github and fbcode
python test/test_quantization.py
TestFxNumericSuiteNShadows.test_custom_functions_and_tracer
Differential Revision: [D41723892](https://our.internmc.facebook.com/intern/diff/D41723892/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90153
Approved by: https://github.com/vkuzo
