Add Golang NACK Backoff support icon in client matrix (#1026)

Author: geniusjoe

data/matrix.js

@@ -445,7 +445,7 @@ module.exports = {
           Feature: "NACK Backoff",
           Java: 2,
           "C++": 0,
-          Go: 0,
+          Go: 2,
           Python: 0,
           Nodejs: 0,
           "C#/DotPulsar": 0,