feat: Update to Apollo Server 2.0

[aldeed]

Impact: minor
Type: feature

Changes

• Updated to Apollo Server 2.0, which has a different way of creating and initializing the server, but the end result isn't any different to clients using the /graphql-alpha endpoint
• Apollo 2.0 now ships with GraphQL Playground instead of GraphiQL. By default it's on the same URL as the GraphQL endpoint (when in dev mode only), so I just kept the default for now. Unlike the old GraphiQL, GraphQL Playground does not automatically know who you are logged in as, so you need to set the Authorization header in the UI.
• Apollo 2.0 now has a test client, which allows us to query it for integration tests without actually listening on a port. I've update the TestApp class and integration tests to use this, and removed the no-longer-needed find-free-port package.

Breaking changes

• /graphiql route will no longer show the GraphiQL UI. Instead /graphql-alpha route, when you GET it through a browser, will show the GraphQL Playground UI.

Testing

1. Verify that you see GraphQL Playground when you go to /graphql-alpha in a browser. Make sure you can query from it. You should be able to query authenticated by setting the Authorization header in the playground Headers panel. You can get your auth token by examining the headers being sent with the GraphQL POST in storefront starter kit.
2. Do some basic smoke tests on a connected storefront, including logging in and out.