Support scoped data fetching in GQL API

[lukashornych]

Add support for inScope require constraint into queries in GraphQL API.

Some require constraints (check docs) supports to be surrounded with inScope require constraints allow an user to require scoped data only within specified scope. We need this mechanism in GraphQL API, but GraphQL API doesn't provide access to the most of the require constraints directly, but rather via output fields. Therefore, we need some tooling on top of the output fields.

Possible solutions that come to mind:

• custom directives like in Conditional contents / GraphQL directives support #474
• union types for extra results and so on

Will be implemented in conjunction with #474