lnrpc: Add optional delivery addresss to close channel

This commit is adapted from @Bluetegu's original
pull request #1462.

lnrpc/rpc.proto

@@ -1557,6 +1557,14 @@ message CloseChannelRequest {
 
     /// A manual fee rate set in sat/byte that should be used when crafting the closure transaction.
     int64 sat_per_byte = 4;
+
+    /*
+    An optional address to send funds to in the case of a cooperative close.
+    If the channel was opened with an upfront shutdown script and this field
+    is set, the request to close will fail because the channel must pay out
+    to the upfront shutdown addresss.
+    */
+    string delivery_address = 5 [json_name = "delivery_address"];
 }
 
 message CloseStatusUpdate {

lnrpc/rpc.swagger.json

@@ -494,6 +494,13 @@
             "required": false,
             "type": "string",
             "format": "int64"
+          },
+          {
+            "name": "delivery_address",
+            "description": "An optional address to send funds to in the case of a cooperative close.\nIf the channel was opened with an upfront shutdown script and this field\nis set, the request to close will fail because the channel must pay out\nto the upfront shutdown addresss.",
+            "in": "query",
+            "required": false,
+            "type": "string"
           }
         ],
         "tags": [