Append nullable withdrawalTxId field to Trade proto message

The withdrawalTxId field will be set in TradeManager#onWithdrawRequest
upon successful trade completion and withdrawal of funds.

Persisting withdrawalTxId will allow the api and ui to find the withdrawalTxId
for a completed trade after the seller withdraws funds to an external wallet.
In turn, the withdrawal tx's memo field will be accessible in a new (todo)
api getTx(txID) api method.

Changed:

- Appended field 'string withdrawal_tx_id = 40' to pb.proto's Trade message.

- Added nullable 'String withdrawalTxId' to Trade entity class.

- Added trade.setWithdrawalTxId(transaction.getTxId().toString()) in
  TradeManager#onWithdrawRequest's callback.

core/src/main/java/bisq/core/trade/Trade.java

@@ -317,6 +317,10 @@ public static protobuf.Trade.TradePeriodState toProtoMessage(Trade.TradePeriodSt
     @Getter
     @Setter
     private String payoutTxId;
+    @Nullable
+    @Getter
+    @Setter
+    private String withdrawalTxId;
     @Getter
     @Setter
     private long tradeAmountAsLong;
@@ -554,6 +558,7 @@ public Message toProtoMessage() {
         Optional.ofNullable(takerFeeTxId).ifPresent(builder::setTakerFeeTxId);
         Optional.ofNullable(depositTxId).ifPresent(builder::setDepositTxId);
         Optional.ofNullable(payoutTxId).ifPresent(builder::setPayoutTxId);
+        Optional.ofNullable(withdrawalTxId).ifPresent(builder::setWithdrawalTxId);
         Optional.ofNullable(tradingPeerNodeAddress).ifPresent(e -> builder.setTradingPeerNodeAddress(tradingPeerNodeAddress.toProtoMessage()));
         Optional.ofNullable(contract).ifPresent(e -> builder.setContract(contract.toProtoMessage()));
         Optional.ofNullable(contractAsJson).ifPresent(builder::setContractAsJson);
@@ -587,6 +592,7 @@ public static Trade fromProto(Trade trade, protobuf.Trade proto, CoreProtoResolv
         trade.setTakerFeeTxId(ProtoUtil.stringOrNullFromProto(proto.getTakerFeeTxId()));
         trade.setDepositTxId(ProtoUtil.stringOrNullFromProto(proto.getDepositTxId()));
         trade.setPayoutTxId(ProtoUtil.stringOrNullFromProto(proto.getPayoutTxId()));
+        trade.setWithdrawalTxId(ProtoUtil.stringOrNullFromProto(proto.getWithdrawalTxId()));
         trade.setContract(proto.hasContract() ? Contract.fromProto(proto.getContract(), coreProtoResolver) : null);
         trade.setContractAsJson(ProtoUtil.stringOrNullFromProto(proto.getContractAsJson()));
         trade.setContractHash(ProtoUtil.byteArrayOrNullFromProto(proto.getContractHash()));
@@ -1124,6 +1130,7 @@ public String toString() {
                 ",\n     takerFeeTxId='" + takerFeeTxId + '\'' +
                 ",\n     depositTxId='" + depositTxId + '\'' +
                 ",\n     payoutTxId='" + payoutTxId + '\'' +
+                ",\n     withdrawalTxId='" + withdrawalTxId + '\'' +
                 ",\n     tradeAmountAsLong=" + tradeAmountAsLong +
                 ",\n     tradePrice=" + tradePrice +
                 ",\n     tradingPeerNodeAddress=" + tradingPeerNodeAddress +

core/src/main/java/bisq/core/trade/TradeManager.java

@@ -497,6 +497,7 @@ public void onSuccess(@javax.annotation.Nullable Transaction transaction) {
                     onTradeCompleted(trade);
                     trade.setState(Trade.State.WITHDRAW_COMPLETED);
                     getTradeProtocol(trade).onWithdrawCompleted();
+                    trade.setWithdrawalTxId(transaction.getTxId().toString());
                     requestPersistence();
                     resultHandler.handleResult();
                 }

proto/src/main/proto/pb.proto

@@ -1450,6 +1450,7 @@ message Trade {
     string counter_currency_extra_data = 37;
     string asset_tx_proof_result = 38; // name of AssetTxProofResult enum
     string uid = 39;
+    string withdrawal_tx_id = 40;
 }
 
 message BuyerAsMakerTrade {