Service Network

Provide users the ability to specify upstream and downstream dependencies for their services. This could be useful for microservice architectures where numerous individual services may interact with one another.

example:

```yml
name: service2
service:
upstream:
- config:
type: webserver
name: service1
- config:
type: event
name: service1-topic
downstream:
- config:
type: webserver
name: service3
healthcheck: "/health"
```

This will allow us to build dependency and health graphs for all services and dependencies