lnrpc: add first hop custom records to RPC payment info

lnrpc/lightning.proto

@@ -4162,6 +4162,12 @@ message Payment {
     uint64 payment_index = 15;
 
     PaymentFailureReason failure_reason = 16;
+
+    /*
+    The custom TLV records that were sent to the first hop as part of the HTLC
+    wire message for this payment.
+    */
+    map<uint64, bytes> first_hop_custom_records = 17;
 }
 
 message HTLCAttempt {

lnrpc/lightning.swagger.json

@@ -6417,6 +6417,14 @@
         },
         "failure_reason": {
           "$ref": "#/definitions/lnrpcPaymentFailureReason"
+        },
+        "first_hop_custom_records": {
+          "type": "object",
+          "additionalProperties": {
+            "type": "string",
+            "format": "byte"
+          },
+          "description": "The custom TLV records that were sent to the first hop as part of the HTLC\nwire message for this payment."
         }
       }
     },

lnrpc/routerrpc/router.swagger.json

@@ -1095,6 +1095,14 @@
         },
         "failure_reason": {
           "$ref": "#/definitions/lnrpcPaymentFailureReason"
+        },
+        "first_hop_custom_records": {
+          "type": "object",
+          "additionalProperties": {
+            "type": "string",
+            "format": "byte"
+          },
+          "description": "The custom TLV records that were sent to the first hop as part of the HTLC\nwire message for this payment."
         }
       }
     },

lnrpc/routerrpc/router_backend.go

@@ -1697,6 +1697,7 @@ func (r *RouterBackend) MarshallPayment(payment *channeldb.MPPayment) (
 		Htlcs:                 htlcs,
 		PaymentIndex:          payment.SequenceNum,
 		FailureReason:         failureReason,
+		FirstHopCustomRecords: payment.Info.FirstHopCustomRecords,
 	}, nil
 }