Add foods index endpoint

As a user,

I should be able to request a list of all foods in the system from the endpoint /api/v1/foods.

The endpoint should result in a status code of 200, and each food item should match the following format:
```
{
"id": 1,
"name": "Banana",
"calories": 250
}
```

- [x] Tested
- [x] Documented