construction fails for depth around > 200 / resource exhaustion?

# Reporting issues with GraphQL-core 3
In my tests the construction of a deep request tree fails with recursion problems.
The problem is a recursive approach in the generation of the graphql request tree (this is why I created the test).

Next to denial of service it is most probably possible to cause resource exhaustion attacks by passing big graphs.

There should be two changes:

- a "stack free" (not really stack free but the recursion depth is drastically reduced) approach in generating the input graph. I did something with generators in my project: graphene-protector:
https://github.com/devkral/graphene-protector
- a node limit after which the generation of the input graph is stopped with an error

I am not sure if the cost spec ( https://ibm.github.io/graphql-specs/cost-spec.html ) can fix this. The changes must take place while generating the requested input graph