@mock existing schema

Possibly via schema delegation or transforms, it _may_ be possible to add a `@mock` annotation to an existing schema and replace the resolver.

A couple things to look into:

- How does `@skip` and `@include` work?
- Does `addMock...` or `addRootSchemaResolver` or whatever allow for there to be a pass-through function to mock anything (as long as the `info` object has the decorator?)
- Do schema transforms allow for customizing the request/response, to possibly stitch together the non-mock portions with a mocked portion?
> https://www.apollographql.com/docs/graphql-tools/schema-transforms.html