Add garnish to ingredients system

If I have fresh mint going bad in my fridge I should be able to search and see what other drinks use fresh mint as a garnish. This means adding ingredient objects to the garnish. How this should be implemented requires some discussion. Either a complete overhaul or an ability to list that an ingredient is for the garnish. There is some balance here between the ingredients, instructions, and garnish of a drink that needs more thought.

Start by tracing how the ingredients, instructions, and garnish of a drink are currently represented and how ingredient searches find drinks. Compare the two proposed approaches: a broader model overhaul or listing garnish ingredients separately. Done means fresh mint and other garnish ingredients can be searched to find drinks that use them, with the relationship between ingredients, instructions, and garnish clearly defined.

Written by the indexing model from the issue text.