fastai_oxford_pets update fastaiv2

I loved your notebook!!
@mattmcclean and @kwwaikar could you please update the tutorial to fastai v2?
The new version of the library was recently released and your tutorial is great but outdated. I updated the code and training works, but having trouble with the input_fn function to make it work when it comes to deployment, i.e. the endpoint is having trouble in deserializing the json / jpeg image. Should be a very quick fix for the awesome fastai community https://drive.google.com/file/d/1hhFoljBME6uh89uQmjaBTDFaZYugVyLu/view?usp=sharing

Start with the fastai_oxford_pets tutorial and inspect its input_fn and deployment endpoint path, using the linked example as context. Run the notebook and deployment flow to reproduce JSON/JPEG deserialization, then verify the tutorial works with fastai v2 and the endpoint accepts the documented inputs.

Written by the indexing model from the issue text.