introduce scan context (#4373)

* introduce scan context

* minor

* add joined errors to resultevents

* change `executor` funcs' signature

* fix tests

* join errors in `LogError` func

* change func signature

* add guard

pkg/protocols/javascript/js.go

@@ -635,6 +635,7 @@ func (request *Request) MakeResultEventItem(wrapped *output.InternalWrappedEvent
 		Response:         types.ToString(wrapped.InternalEvent["response"]),
 		IP:               types.ToString(wrapped.InternalEvent["ip"]),
 		TemplateEncoded:  request.options.EncodeTemplate(),
+		Error:            types.ToString(wrapped.InternalEvent["error"]),
 	}
 	return data
 }