gulp: disable graphql-codegen's watch feature

Created by: LawnGnome

Due to https://github.com/dotansimha/graphql-code-generator/issues/1796, gulp is currently consuming a non-trivial amount of a CPU core watching for updates that regenerate the GraphQL operations files. Let's use Chokidar directly (via Gulp) and then we can be smarter about when we actually trigger the several second generation process.