feature request: hierarchal blueprint support or dependent blueprint support

@elwayman02 and I were discussing this and I wanted to capture the essence of our conversation in this feature request.

Jordan has a use case where he wants to write a blueprint for the collection of Ember addon projects his team maintains. The thing is though he needs another addon's blueprint to be generated before running his blueprint so that it can layer changes on top of that. From my understanding of the `ember-cli-update` codebase, it will only install and generate one blueprint per run.

Some of the conversation items we had were:

- How will version management work for dependent packages containing the blueprints?
- How should the dependencies be defined?
- How will ember-cli-update prompt for updates