lnrpc: describe request replacement in API docs

This commit updates the comments in the proto file to mention the new
behavior of also being able to replace request messages.

lnrpc/lightning.swagger.json

@@ -4682,12 +4682,12 @@
         },
         "replace_response": {
           "type": "boolean",
-          "description": "A boolean indicating that the gRPC response should be replaced/overwritten.\nAs its name suggests, this can only be used as a feedback to an intercepted\nresponse RPC message and is ignored for feedback on any other message. This\nboolean is needed because in protobuf an empty message is serialized as a\n0-length or nil byte slice and we wouldn't be able to distinguish between\nan empty replacement message and the \"don't replace anything\" case."
+          "description": "A boolean indicating that the gRPC message should be replaced/overwritten.\nThis boolean is needed because in protobuf an empty message is serialized as\na 0-length or nil byte slice and we wouldn't be able to distinguish between\nan empty replacement message and the \"don't replace anything\" case."
         },
         "replacement_serialized": {
           "type": "string",
           "format": "byte",
-          "description": "If the replace_response field is set to true, this field must contain the\nbinary serialized gRPC response message in the protobuf format."
+          "description": "If the replace_response field is set to true, this field must contain the\nbinary serialized gRPC message in the protobuf format."
         }
       }
     },