Improve release procedure

Currently we have a rigid release.

When we tag a release, packages get released to the public right away.

We don't officially announce the release until we deploy to staging and then to production. Also deploy the blog post.

This is a problem because the packages are accessible regardless of what we find during the deploy. This has caused both problems and confusion.

During a short brainstorming session with @pcarranza we decided to try and leverage more of our CI. The changes should be minimal to both the Build Team and Production Team.

Idea is to:

1. Instead of uploading the package to S3, we would push package as artifact
2. Leverage enivronments feature to fetch the uploaded artifact
3. In staging step, push to a separate package repository. This would be the minimal change for Production team, just switch out the repository urls in staging
4. Once confirmed that all is ok, in a manual production step we would fetch the same artifact and push it to the public repo.
5. The last step is a manual task for RM, push the button to push to public repository.

TODO:

• Add packages as artifacts https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1404
• After package is built, add environment support(named staging) in CI
• Add code that'll push all packages to a temporary repository(OK to be private at start). This needs to be idempotent.
• During this stage we can also build a temp Docker image and push it to registry
• Create manual environment(named production) which will download the artifacts and push to correct public repo