Support @defer and @stream directives

[jakobvase]

Hi Lacinia! We're using Lacinia, and it's a pleasure.

I wonder if you've considered adding support for the @stream and @defer directives. They are stage 2 RFC for the spec and allow for much improved UX, since the client can tell the server that parts of the query are less important and can be delivered in a second round, when necessary.

blog post by the champion here: https://graphql.org/blog/2020-12-08-improving-latency-with-defer-and-stream-directives/
rfc here: https://github.com/graphql/graphql-wg/blob/main/rfcs/DeferStream.md
spec merge request here: graphql/graphql-spec#742