can disable expensive suggestions

[yanns]

By overriding the default QueryValidator, one can disable or add a cache for the suggested fields.
Fixes #497

[agourlay]

This is a nice way to avoid the problem 👍

[kiranbayram]

This looks good 👏 , any information on when this will be released ?

[yanns]

https://github.com/sangria-graphql/sangria/releases/tag/v2.0.1

[yanns]

How to disable expensive suggestions:

  val queryValidationRules = QueryValidator.allRules.map {
    case _: KnownTypeNames => new KnownTypeNames(suggestion = SuggestionFunction.Disabled)
    case o => o
  }

  val executor = Executor(
    queryValidator = ruleBased(queryValidationRules),
    [...]
  )