[Go Function API] Need automated integration test to verify Go functions behave properly

[devinbost]

We need to ensure that Go Functions behave properly when run from the Pulsar FunctionManager and other classes responsible for controlling Go Function instances.

[jiazhai]

Thanks @devinbost for the issue and fix. Thanks @wolfstudy for the review of PR.

[tisonkun]

Closed by #6104.