Support @defer?

[tomhoule]

https://blog.apollographql.com/introducing-defer-in-apollo-server-f6797c4e9d6e

This is not part of the spec. The parts that are not fetched yet could be None, and the patches would have that field as a root. How could we support this:

• In the core library?
• In a transport-specific way? (e.g. with websockets for the deferred data in browsers)