looprpc: expose server message to clients

interface.go

@@ -248,6 +248,10 @@ type LoopInSwapInfo struct { // nolint
 	// HtlcAddressNP2WSH contains the nested segwit swap htlc address,
 	// where the loop-in funds may be paid.
 	HtlcAddressNP2WSH btcutil.Address
+
+	// ServerMessages is the human-readable message received from the loop
+	// server.
+	ServerMessage string
 }
 
 // LoopOutSwapInfo contains essential information of a loop-out swap after the
@@ -259,6 +263,10 @@ type LoopOutSwapInfo struct { // nolint:golint
 	// HtlcAddressP2WSH contains the native segwit swap htlc address that
 	// the server will publish to.
 	HtlcAddressP2WSH btcutil.Address
+
+	// ServerMessages is the human-readable message received from the loop
+	// server.
+	ServerMessage string
 }
 
 // SwapInfoKit contains common swap info fields.