make it automatic to include types implementing an interface in the graphql schema

[axiomofjoy]

In order to use interfaces as a return type, I have to explicitly include all of the types implementing the interface via the types argument in strawberry.Schema in order for those types to be included in the schema. This is inconvenient. I would like for strawberry to automatically detect these types for me (e.g., by looking for __subclasses__ of the implementing type), or at least have utilities that make this easier.

[erikwrede]

Interesting idea! I built a quick PoC in #3686. However, it won't be as easy as depicted there to implement this. Taking the discussion to discord.