taprpc: add label field to AssetTransfer and SendEvent

Author: ffranr

rpcserver.go

@@ -3662,6 +3662,7 @@ func marshalOutboundParcel(
 		AnchorTxBlockHeight: parcel.AnchorTxBlockHeight,
 		Inputs:              rpcInputs,
 		Outputs:             rpcOutputs,
+		Label:               parcel.Label,
 	}, nil
 }
 
@@ -4178,6 +4179,7 @@ func marshalSendEvent(event fn.Event) (*taprpc.SendEvent, error) {
 		SendState:             e.SendState.String(),
 		VirtualPackets:        make([][]byte, len(e.VirtualPackets)),
 		PassiveVirtualPackets: make([][]byte, len(e.PassivePackets)),
+		TransferLabel:         e.TransferLabel,
 	}
 
 	if e.Error != nil {

taprpc/assetwalletrpc/assetwallet.swagger.json

@@ -926,6 +926,10 @@
           "type": "integer",
           "format": "int64",
           "description": "The block height of the blockchain block that contains the anchor\ntransaction. If the anchor transaction is still unconfirmed, this value\nwill be 0."
+        },
+        "label": {
+          "type": "string",
+          "description": "An optional short label for the transfer. This label can be used to track\nthe progress of the transfer via the logs or an event subscription.\nMultiple transfers can share the same label."
         }
       }
     },