Add go fmt CI check

Right now, we occasionally notice that checked in files have not been formatted properly (e.g. https://github.com/apache/beam/pull/16973). It would be nice to catch these as a precommit check (it could be something as simple as a quick Actions or Jira job that runs:

```

go fmt sdks/go/...
git diff-index --quiet HEAD – || (echo "Run go fmt before checking in changes" && exit 1)}}

```

That way we push the work to the original authors and let robots enforce linting