Introduce new GraphQL directive to restrict access to endpoint based on Feature Flag values.

Example:

type Query {
  doSomething: String! @ff(flags: ["SOME_FLAG", "SOME_OTHER_FLAG"])
}

This definition will make queries to doSomething throw neither one of the feature flags is set.

Optionally introduce a softFail option that will resolve to null instead of returning an error:

type Query {
  doSomething: String @ff(flags: ["SOME_FLAG", "SOME_OTHER_FLAG"], softFail: true)
}

This can be helpful for queries happening super early, even before (or while) retrieving the FFs in the frontend.