Handling link in T-API topology

The set of rpcs used to populate links between ROADMs and Xponders has been replicated to do the same thing with T-API topology. If it makes sense in the long term where T-API topology may includes some nodes coming from OpenROADM domain, but also some additional NEs coming from a T-API domain, in the short term, where T-API topology is a replication of the OR topology in the T-API format, we should try to import all existing links from the OR topology.

A listener shall be created on openroadm-topology so that links appearing in openroadm-topology are automatically populated.

Acceptance criteria : the code is submitted for review and does not bring any regression. Junit tests are complemented to address new features.