NetBird SSH (#361)

This PR adds support for SSH access through the NetBird network
without managing SSH skeys.
NetBird client app has an embedded SSH server (Linux/Mac only) 
and a netbird ssh command.

management/server/updatechannel.go

@@ -9,6 +9,7 @@ import (
 type UpdateMessage struct {
 	Update *proto.SyncResponse
 }
+
 type PeersUpdateManager struct {
 	peerChannels map[string]chan *UpdateMessage
 	channelsMux  *sync.Mutex