First-Class support for @stream/@defer in strawberry

This issue is going to collect all necessary steps for an awesome stream and defer devX in Strawberry 🍓

First steps collected today together in discovery session with @patrick91 @bellini666

ToDos for an initial support:

• Add support for [async/sync] generators in return types
• Make sure GraphQLDeferDirective, GraphQLStreamDirective, are in the GQL-Core schema
  Flag in Schema(query=Query, config={enable_stream_defer: False}) - default true
• Add incremental delivery support to all the views
• FastAPI integration -> Maybe in the Async Base View?
• Explore Sync View Integration

long term goals

incomplete list of problems / design improvement potential of the current raw implementation

Problem: streaming / n+1 -> first-level dataloaders are no longer working as every instance is resolved 1:1

Possible solutions

• dig deeper into [graphql-js] Yielding batches of results in resolver functions graphql/defer-stream-wg#40
• custom query execution plan engine
• Add @streamable directive to schema fields automatically if field is streamable, including custom validation rule

Some playground code: https://gist.github.com/erikwrede/993e1fc174ee75b11c491210e4a9136b