routerrpc: add htlc notifier subscribed event

lnrpc/routerrpc/router.swagger.json

@@ -1317,6 +1317,9 @@
         },
         "link_fail_event": {
           "$ref": "#/definitions/routerrpcLinkFailEvent"
+        },
+        "subscribed_event": {
+          "$ref": "#/definitions/routerrpcSubscribedEvent"
         }
       },
       "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]"
@@ -1748,6 +1751,9 @@
         }
       }
     },
+    "routerrpcSubscribedEvent": {
+      "type": "object"
+    },
     "routerrpcUpdateChanStatusRequest": {
       "type": "object",
       "properties": {