[day-03] expose id in user schema

Use uuid custom scalar to represent the user id.

lib/wabanex_web/schema/types/user.ex

@@ -1,8 +1,11 @@
 defmodule WabanexWeb.Schema.Types.User do
   use Absinthe.Schema.Notation
 
+  import_types WabanexWeb.Schema.Types.Custom.UUID4
+
   @desc "Logic user representation"
   object :user do
+    field :id, non_null(:uuid4)
     field :name, non_null(:string)
     field :email, non_null(:string)
   end