lnrpc: add incoming chan list to BlindedPathConfig

Add an option to the addinvoice rpc which allows to specify
the blinded path via a list of chained channels.

lnrpc/lightning.swagger.json

@@ -3688,6 +3688,14 @@
             "format": "byte"
           },
           "description": "A list of node IDs of nodes that should not be used in any of our generated\nblinded paths."
+        },
+        "incoming_channel_list": {
+          "type": "array",
+          "items": {
+            "type": "string",
+            "format": "uint64"
+          },
+          "description": "The chained channels list specified via channel id (separated by commas),\nstarting from a channel owned by the receiver node."
         }
       }
     },