Removes gitlab based scheme, use git tag scheme

We have decided to use normal tag scheme, and only change GitLab CE Auto DevOps CI template as needed (rather than have that auto-increment and risk us forgetting to release ahead of GitLab CE)

Based on discussion from #9 (comment 191003945)

So say we tag v1.0.0, the release-tag job will then tag the docker image as

registry.gitlab.com/gitlab-org/cluster-integration/auto-deploy-image:v1.0.0

Which is what we will use as the image: in https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/ci/templates/Jobs/Deploy.gitlab-ci.yml

Closes #9 (closed)

Testing

Pipeline (for tag): https://gitlab.com/gitlab-org/cluster-integration/auto-deploy-image/pipelines/72812135 ✅