feat: make MDNS failure on start non-fatal (#1310)

* feat: make MDNS failure on start non-fatal

- if discovery.NewMdnsService errors on start, show warning "error message, MDNS service will be disabled"
- same as setting MDNSInterval to 0: NewCluster is still created and daemon runs, but without MDNS

cluster.go

@@ -141,10 +141,10 @@ func NewCluster(
 	if cfg.MDNSInterval > 0 {
 		mdns, err := discovery.NewMdnsService(ctx, host, cfg.MDNSInterval, mdnsServiceTag)
 		if err != nil {
-			cancel()
-			return nil, err
+			logger.Warnf("mDNS could not be started: %s", err)
+		} else {
+			mdns.RegisterNotifee(peerManager)
 		}
-		mdns.RegisterNotifee(peerManager)
 	}
 
 	c := &Cluster{