declarative services

[arlac77]

make service dependencies declarable:

 {
  "name": "my-step",
  "endpoints" : {},
  "services": {
    "listener": {
      "name": "default-listener",
      "type": "koa"
    }
  }
}

my-step requires a service named listener of type koa.

In the step the service is called listener in the service-registration it is called default-listener
and the implementation is a koa.

short form local name and registration name are equal

 {
  "name": "my-step",
  "endpoints" : {},
  "services": {
    "listener": "koa"
  }
}

The service will get an property after the service name
and the service will be started when the step get started

So that a step implementation method can write the following statement:

   this.listener.  /* umplementation specific follows */ server.listen(....)