Write query that pulls fruit/vegetable info from Trefle API

In Plants app, write handler to pull data from [Trefle API](https://trefle.io/). Ultimately we want a user of this (gardenbuilder-backend) to write a GraphQL query, passing in a fruit or vegetable name ("Tomato", for example). This handler/function would then query all of the tomato varieties from the Treffle API, return them, and then return all the tomato varieties to the user/graphql interface.