fix: restore observability instrumentation in MasterClient

During the refactoring, several important stats counters and logging
statements were accidentally removed from tryConnectToMaster. These are
critical for monitoring and debugging the health of master client connections.

Restored instrumentation:
1. stats.MasterClientConnectCounter("total") - tracks all connection attempts
2. stats.MasterClientConnectCounter(FailedToKeepConnected) - when KeepConnected stream fails
3. stats.MasterClientConnectCounter(FailedToReceive) - when Recv() fails in loop
4. stats.MasterClientConnectCounter(Failed) - when overall gprcErr occurs
5. stats.MasterClientConnectCounter(OnPeerUpdate) - when peer updates detected

Additionally restored peer update logging:
- "+ filer@host noticed group.type address" for node additions
- "- filer@host noticed group.type address" for node removals
- Only logs updates matching the client's FilerGroup for noise reduction

This information is valuable for:
- Monitoring cluster health and connection stability
- Debugging cluster membership changes
- Tracking master failover and reconnection patterns
- Identifying network issues between clients and masters

No functional changes - purely observability restoration.

weed/wdclient/masterclient.go

@@ -157,6 +157,8 @@ func (mc *MasterClient) tryAllMasters(ctx context.Context) {
 }
 
 func (mc *MasterClient) tryConnectToMaster(ctx context.Context, master pb.ServerAddress) (nextHintedLeader pb.ServerAddress) {
+	glog.V(1).Infof("%s.%s masterClient Connecting to master %v", mc.FilerGroup, mc.clientType, master)
+	stats.MasterClientConnectCounter.WithLabelValues("total").Inc()
 	gprcErr := pb.WithMasterClient(true, master, mc.grpcDialOption, false, func(client master_pb.SeaweedClient) error {
 		ctx, cancel := context.WithCancel(ctx)
 		defer cancel()
@@ -164,6 +166,7 @@ func (mc *MasterClient) tryConnectToMaster(ctx context.Context, master pb.Server
 		stream, err := client.KeepConnected(ctx)
 		if err != nil {
 			glog.V(1).Infof("%s.%s masterClient failed to keep connected to %s: %v", mc.FilerGroup, mc.clientType, master, err)
+			stats.MasterClientConnectCounter.WithLabelValues(stats.FailedToKeepConnected).Inc()
 			return err
 		}
 
@@ -205,6 +208,7 @@ func (mc *MasterClient) tryConnectToMaster(ctx context.Context, master pb.Server
 			resp, err := stream.Recv()
 			if err != nil {
 				glog.V(0).Infof("%s.%s masterClient failed to receive from %s: %v", mc.FilerGroup, mc.clientType, master, err)
+				stats.MasterClientConnectCounter.WithLabelValues(stats.FailedToReceive).Inc()
 				return err
 			}
 
@@ -227,6 +231,14 @@ func (mc *MasterClient) tryConnectToMaster(ctx context.Context, master pb.Server
 				update := resp.ClusterNodeUpdate
 				mc.OnPeerUpdateLock.RLock()
 				if mc.OnPeerUpdate != nil {
+					if update.FilerGroup == mc.FilerGroup {
+						if update.IsAdd {
+							glog.V(0).Infof("+ %s@%s noticed %s.%s %s\n", mc.clientType, mc.clientHost, update.FilerGroup, update.NodeType, update.Address)
+						} else {
+							glog.V(0).Infof("- %s@%s noticed %s.%s %s\n", mc.clientType, mc.clientHost, update.FilerGroup, update.NodeType, update.Address)
+						}
+						stats.MasterClientConnectCounter.WithLabelValues(stats.OnPeerUpdate).Inc()
+					}
 					mc.OnPeerUpdate(update, time.Now())
 				}
 				mc.OnPeerUpdateLock.RUnlock()
@@ -238,6 +250,7 @@ func (mc *MasterClient) tryConnectToMaster(ctx context.Context, master pb.Server
 		}
 	})
 	if gprcErr != nil {
+		stats.MasterClientConnectCounter.WithLabelValues(stats.Failed).Inc()
 		glog.V(1).Infof("%s.%s masterClient failed to connect with master %v: %v", mc.FilerGroup, mc.clientType, master, gprcErr)
 	}
 	return nextHintedLeader