feat: examples/golang/waku.go add new example (#2559)

* examples/golang/waku.go: add new example
* waku.go: Richard recommendations
#2559 (review)
Not addressing points 3 and 9 in this commit.
* waku.go: allow setting separate callback methods per WakuNode instance
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Co-authored-by: richΛrd <info@richardramos.me>