Gitlab-CI: Publish Release on Tag

Part of #3 (closed) - we need to publish rendered files for easy consumption by non-jsonnet users.

Skipping automatic semver tag bumping for now...

General CI:

• remove dummy stage, we don't have any changes: restrictions and can run jsonnet renderer on any change.
• rename stages

When TAG manually created kickoff CI to:

• render jsonnet and test with prometheus (above job)
• tar up rendered manifests (dashboards, prom rules, podmonitor, etc)
• upload to Gitlab generic package registry
• publish release