RFC: First class mocking support

[JoviDeCroock]

Summary

Currently we have a documentation page around mocking fields/entities that aren't implemented yet, we could take this further by integrating faker.js we could make this as easy as adding { mock: 'phoneNumber' } or something similar which would mock the value when there isn't one present on the payload.

Proposed Solution

We extend the pothos field builder API with a mock option that integrates faker, when no value is present we invoke the faker method and mock the value.