move Golang extension from contrib to standard

### Motivation
Make people use the standard version with confidence.
Some people have expressed concerns about the contrib version, i.e. [the thread in enovy-go slack channel](https://envoyproxy.slack.com/archives/C04QNSXC7U0/p1701921159504429).

### Status
The latest envoy 1.28.0 should be stable enough.
All knowned bug are fixed in envoy 1.28.0. And no new bugs reported since 1.28.0.

Nearly ~100 improvements, and ~5 bugfixes since first merged in contrib.
i.e. retired the `GODEBUG=cgocheck=0` env requirement.

### Test

- [x] fuzzer: https://github.com/envoyproxy/envoy/pull/25884
- [ ] test coverage
- [x] test flake: https://github.com/envoyproxy/envoy/issues/31654

### Doc

There are some baisc doc about how to develop and build plugin, and examples for how to implement golang plugins.

- [ ] need more detailed doc about the Go APIs, for implementing Golang plugins.

### Question
In addition to these TODOs, what else needs to address? Or, any other requirements?
cc @mattklein123 @alyssawilk @phlax @wbpcode Any advice & guidance? Thanks very much!

Maybe it could be done in the 1.31 release? if there are no big blocking issue.