Include implementing types for interface in schema

[observant2]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no
Version/Branch	0.13

In the docs it says that types implementing interfaces need to be declared explicitly via YAML if no resolvers are present. On the other hand GraphQLBundle can serve them without being declared (when at least one implementing type is there, I don't know how it does that). However we need all implementing types of all interfaces (we have a lot of those) explicitly declared in the schema, because we have a proxy that needs to know all resolvable types. Is it possible to automatically include all implementing types in the schema although they're only referenced via their interface in the schema? That way we could make sure that our application won't break because we missed adding the types in a yaml far away from the sources.

Moved from here.