Help text: This is used to uniquely identify an edge node in a ProGet Hub instance.
Back-end changes:
* Add `X-ProGet-InstanceId` FeedSyncHeader, send in FeedReplicator for Edge Nodes
* In FeedReplicator, if `ProGetConfig.Licensing.EdgeNodeId` is empty, generate a new GUID
* Add InstanceID column to `ReplicationClients` table and populate
* Adjust logic as appropriate on UI to use this like we currently use IP address