Add support for component outputs

[davidthor]

Component outputs are a great way for components to provide values to upstream consumers. Sometimes the data will be static (e.g. an event topic), and other times it will be dynamic with a different value provided to each consumer (e.g. credentials).

The component spec

# architect/dependency
version: v2

deployments:
  main:
    image: my-image:latest
    command: npm start

services:
  public:
    deployment: main
    port: 8080
  admin:
    deployment: main
    port: 8081

outputs:
  my-event-topic:
    description: The topic I publish events to
    value: my-topic-name
  credentials:
    description: Unique credentials to access my service
    sensitive: true
    on:
      create:
        image: my-image:latest
        command: ./gen-credentials.sh
        environment:
          ADMIN_ADDR: ${{ services.admin.url }}

---
# architect/consumer
version: v2

dependencies:
  dependency: architect/dependency

deployments:
  main:
    image: test:latest
    environment:
      PUBLIC_ADDR: ${{ dependencies.dependency.services.public.url }}
      TOPIC: ${{ dependencies.dependency.outputs.my-event-topic.value }}
      CREDENTIALS: ${{ dependencies.dependency.outputs.credentials.value }}

Implementation notes

• The above schema assumes that the outputs.*.on.create will launch a task that has access to the public service. This should operate the same way other tasks and cronjobs work today.
• The credentials should be the only thing logged to stdout
• The task we actually create should write the stdout contents to a "secret" resource that gets created for each consumer

[davidthor]

I'm not sold on the stdout being used by the hook author as the way to provide the payload for the output. I feel like that cripples any potential to use stdout for debugging related features. I welcome any other suggestions for how this handshake should work.