services module contains the service descriptor of each service within the aggregate.
ProTip: A service descriptor define metadata about a service, including the name of the service’s Docker image and the external resources the service interacts with, for example a Kafka topic, or a Database.
services jar is used by the system tests to discover services in the aggregate.
To avoid dependency hell when running system tests it should be pretty much dependency free.
Because the jar is not shared outside the aggregate, there is no backwards compatibility concerns.