Dockerize a starter golang app and add to stackbox. This will invlove the following steps. 1. Dockerize basic golang app (without any endpoints) **(with multistage build)** 2. Add code folder with Dockerfile to repo 3. Add golang as an option in stackbox.sh Refer to [Angular](https://github.com/Stack-Box/stackbox/pull/53) and [React](https://github.com/Stack-Box/stackbox/pull/60) PRs for more understanding.