[day-03] create resolver to fetch user

This resolver is required to create a graphql query to get users.

lib/wabanex_web/resolvers/user.ex

@@ -0,0 +1,5 @@
+defmodule WabanexWeb.Resolvers.User do
+  alias Wabanex.Users
+
+  def get(%{id: user_id}, _context), do: Users.Get.call(user_id)
+end