feat(examples): add hello_world, update `r/demo/event` #9213

Job	Run time
Run Main (autocounterd) / Go Build / generated	8s
Run Main (autocounterd) / Go Linter / lint	16s
Run Main (autocounterd) / Go Test / test	27s
Run Main (docker-integration) / Go Build / generated	7s
Run Main (docker-integration) / Go Linter / lint	17s
Run Main (docker-integration) / Go Test / test	12s
Run Main (genproto) / Go Build / generated	13s
Run Main (genproto) / Go Linter / lint	37s
Run Main (genproto) / Go Test / test	17s
Run Main (genstd) / Go Build / generated	12s
Run Main (genstd) / Go Linter / lint	36s
Run Main (genstd) / Go Test / test	17s
Run Main (goscan) / Go Build / generated	6s
Run Main (goscan) / Go Linter / lint	22s
Run Main (goscan) / Go Test / test	29s
Run Main (loop) / Go Build / generated	9s
Run Main (loop) / Go Linter / lint	37s
Run Main (loop) / Go Test / test	25s
	5m 47s

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