htlcswitch: add final htlc event to notifier

lnrpc/routerrpc/router.swagger.json

@@ -1168,6 +1168,17 @@
       ],
       "default": "UNKNOWN"
     },
+    "routerrpcFinalHtlcEvent": {
+      "type": "object",
+      "properties": {
+        "settled": {
+          "type": "boolean"
+        },
+        "offchain": {
+          "type": "boolean"
+        }
+      }
+    },
     "routerrpcForwardEvent": {
       "type": "object",
       "properties": {
@@ -1320,6 +1331,9 @@
         },
         "subscribed_event": {
           "$ref": "#/definitions/routerrpcSubscribedEvent"
+        },
+        "final_htlc_event": {
+          "$ref": "#/definitions/routerrpcFinalHtlcEvent"
         }
       },
       "title": "HtlcEvent contains the htlc event that was processed. These are served on a\nbest-effort basis; events are not persisted, delivery is not guaranteed\n(in the event of a crash in the switch, forward events may be lost) and\nsome events may be replayed upon restart. Events consumed from this package\nshould be de-duplicated by the htlc's unique combination of incoming and\noutgoing channel id and htlc id. [EXPERIMENTAL]"