Add experimental support for @defer, @stream, and @live

I’ve just completed implementation of the three new directives mentioned in the GraphQL Futures talk in GraphQL-Go: https://gist.github.com/paralin/f6891bd30eb96e91fba628096af3278c

I now need to enable Apollo-Client to understand these responses.

• A “query” now has a stream of responses (like a subscription) and will need a new NetworkInterface type to enable this kind of streaming transport.
• The “query” ends when the remote server closes the result channel. It’s up to the network interface to understand when this happens and communicate it back to Apollo.
• Any query, even ones that do not use @stream, @defer, or @live can be sent over a streaming channel in the same way. If a query does not require returning data at a later time, the server will just immediately close the channel after returning the initial result.
• Initial result looks identical to how Apollo currently receives results, with the exception of the lack of fields that are deferred in the initial response (those come in later)
• The field path looks like ["regions", 0, "status"] and comes in in extensions.path.

These features are obviously experimental, but I’ve been able to build a real proof of concept of the server end of this in just a couple of days. I’m interested to now get it working properly with Apollo.

[Akryum]

Any progress on supporting @defer on apollo? 😄

[stubailo]

I think this is a good thing to reopen - part of the work for #1941 (Apollo Client 2.0) is supporting multiple results for the same query, which will make supporting @live and @defer pretty easy!