[Issue 4752][docs] Add language tabs and description for Go (#5750)
[Issue 4752][docs] Add language tabs and description for Go (#5750)

### Motivation
Currently, the following features are not available in Go Functions: SerDe, metrics, state storage, user config. 

### Modifications
Add the language-specific tab for Go, and add a sentence "the feature is not available in Go".

merlimat/pulsar,massakam/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,yahoo/pulsar,merlimat/pulsar,yahoo/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar