Add a concept of a recipe

Basically a recipe is just a collection of items you need to buy. when you add "hamburgers" to your grocery list, it would add everything in that recipe (burgers, buns, ketchup, mustard, lettuce).

I'm not sure if this is even a good idea since you don't need everything in the recipe every time (you don't buy ketchup and mustard every time you decide to grill burgers)

No files, tests, or entry points are named. First clarify whether recipes should add all ingredients or support optional items, then locate the grocery-list flow and define the recipe behavior and acceptance criteria before implementation.

Written by the indexing model from the issue text.