gitlab-shell: add bin/hello-world Go executable

• source code in /go/cmd/hello-world
• use bin/compile to create bin/hello-world
• update source instructions, omnibus to run bin/compile

mentioned in issue #124 (closed)

assigned to @jacobvosmaer-gitlab

mentioned in merge request gitlab-shell!127 (merged)

The idea here is for me to get most of the plumbing done so that whoever does the client implementation of SSH forwarding can focus on just that; it's hard enough as it is.

GDK merge request: https://gitlab.com/gitlab-org/gitlab-development-kit/merge_requests/282

If these two merge requests go in we have enough foundation for the client implementation of SSH forwarding I think.

closed via merge request gitlab-shell!127 (merged)