Add: MultipleChoice with Transfer Learning example

[awsaf49]

This PR will add the MultipleChoice example with Transfer Learning using KerasNLP and KerasCore as mentioned in #791 .

Here is the colab demo: Colab

I'm open to open to feedback to make this example more suitable for Keras users.

I didn't run the python autogen.py add_example vision/script_name script as in the examples in this repo, I couldn't see any /ipynb, /md, or /img directories.

[awsaf49]

cc: @fchollet

[fchollet]

Thanks for the PR! Some intiail comments.

[fchollet]

LGTM -- thank you!