Add recipes config & temp hello_world recipe

The non-generated files are:
- infra/config/recipes.cfg
- recipes/recipes.py
- recipes/recipes/hello_world.py
- .gitignore

Then ran command to generate and test everything:
$ python2.7 ./recipes/recipes.py test train

Google-Bug-Id: b/238869100
Change-Id: Ie6e987b87c85ba173b036bf1db74b76b05f22f19