[V2] =>Extend YAML parsing to allow variable references

Problem

Given a YAML Seed file,

projects:
  - name: My Project
    creator_id: <%= @owner.id %>
    namespace_id: <%= @namespace.id %>
    traits:
      - public

project_issues:
  - title: My Issue
    project_id: <%= # cannot reference here %>

Given 1 project and 1 issue, we cannot refer back to any created factory models.

Proposal

Introduce variables to YAML to allow referring back to previously declared models.

Example

projects:
  - _id: my_project
    name: My Project
    creator_id: <%= @owner.id %>
    namespace_id: <%= @namespace.id %>
    traits:
      - public

project_issues:
  - title: My Issue
    project_id: <%= projects.my_project.id %>
    weight: 2

Perhaps use a _id attribute attached that can be used as a unique identifier.