rpcserver: expose ChanStatusFlags in pending close

This commit exposes the ChanStatusFlags inside waitingCloseResp such
that the channel close type is exposed.

lnrpc/lightning.proto

@@ -2312,6 +2312,9 @@ message PendingChannelsResponse {
 
         // Total number of forwarding packages created in this channel.
         int64 num_forwarding_packages = 10;
+
+        // A set of flags showing the current state of the channel.
+        string chan_status_flags = 11;
     }
 
     message PendingOpenChannel {

lnrpc/lightning.swagger.json

@@ -2757,6 +2757,10 @@
           "type": "string",
           "format": "int64",
           "description": "Total number of forwarding packages created in this channel."
+        },
+        "chan_status_flags": {
+          "type": "string",
+          "description": "A set of flags showing the current state of the channel."
         }
       }
     },

rpcserver.go

@@ -3453,6 +3453,7 @@ func (r *rpcServer) PendingChannels(ctx context.Context,
 			Initiator:             rpcInitiator(waitingClose.IsInitiator),
 			CommitmentType:        rpcCommitmentType(waitingClose.ChanType),
 			NumForwardingPackages: int64(len(fwdPkgs)),
+			ChanStatusFlags:       waitingClose.ChanStatus().String(),
 		}
 
 		waitingCloseResp := &lnrpc.PendingChannelsResponse_WaitingCloseChannel{