Collect directives from applications

[mattvb91]

Besides collecting resolvers from corejam applications and merging them, we need to also collect directives that each application defines and merge it into the top level server.

An example of DerShop server export:

const pluginProperties = {
  resolvers,
  directives,
  schemas: ["dershop"],
};

export { getPluginContext } from "./resolvers";

https://www.apollographql.com/docs/apollo-server/schema/creating-directives/#enforcing-access-permissions