Implemement smoke_test.py for pip wheel jobs (#3474)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3474

This script is run by CI after building the executorch wheel. Before
running this, the job will install the matching torch package as well as
the newly-built executorch package and its dependencies.

For now we test the export of a simple model, and try executing it using
the runtime pybindings.

Test Plan:
```
./install_requirements.sh
python build/packaging/smoke_test.py
```

imported-using-ghimport

Reviewed By: mikekgfb

Differential Revision: D56857490

Pulled By: dbort

fbshipit-source-id: e52fdba63dafbe7d653d8696001bf3b21775f493