Add support for creating "user defined" or "manual" links to the enlinkd topology.
Aside from allowing users to enrich the Enlinkd topology, this can also be used as a stop-gap solution for programatically creating links from other sources (i.e. via the integration API).
Users can add create a new link between two nodes using the REST API, and have it immediately appear in the topology map.
These user defined links should also be forwarded via the Kafka producer when created.