rpc: Add PendingOpenChannel to SubscribeChannelEvents

This commit adds PendingOpenChannel to SubscribeChannelEvents stream in
the gRPC API.
This is useful for keeping track of channel openings that Autopilot does.
It can also be used for the non-initator side of a channel opening to keep
track of channel openings.

server.go

@@ -1113,13 +1113,14 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 			// channel bandwidth.
 			return uint16(input.MaxHTLCNumber / 2)
 		},
-		ZombieSweeperInterval:  1 * time.Minute,
-		ReservationTimeout:     10 * time.Minute,
-		MinChanSize:            btcutil.Amount(cfg.MinChanSize),
-		MaxPendingChannels:     cfg.MaxPendingChannels,
-		RejectPush:             cfg.RejectPush,
-		NotifyOpenChannelEvent: s.channelNotifier.NotifyOpenChannelEvent,
-		OpenChannelPredicate:   chanPredicate,
+		ZombieSweeperInterval:         1 * time.Minute,
+		ReservationTimeout:            10 * time.Minute,
+		MinChanSize:                   btcutil.Amount(cfg.MinChanSize),
+		MaxPendingChannels:            cfg.MaxPendingChannels,
+		RejectPush:                    cfg.RejectPush,
+		NotifyOpenChannelEvent:        s.channelNotifier.NotifyOpenChannelEvent,
+		OpenChannelPredicate:          chanPredicate,
+		NotifyPendingOpenChannelEvent: s.channelNotifier.NotifyPendingOpenChannelEvent,
 	})
 	if err != nil {
 		return nil, err