policy-node: Add ability to read custom links at startup

Added support for reading custom links between nodes from
config file, 'policy-node.conf', while starting up the
session manager. The config file should provide an array
with key "links" which contains spa_json_objects with keys
"node" and "peer".
2 jobs for custom-links in 1 minute and 49 seconds
latest
Status Name Job ID Coverage
  Container
passed container_fedora #8580551

00:01:11

 
  Build
passed build_on_fedora #8580552

00:00:38