Determine server's GraphQL spec version

[execveat]

GQLSpection includes three introspection queries for different GraphQL spec versions, but we're not actually using them when requesting introspection from the server.

Implement fallback strategy similar to https://github.com/doyensec/inql/blob/dev/python/inql/scanner/introspection.py#L46 and optionally output the identified GraphQL spec version.