Use Standard Multi-stage build conventions

Overview

During reviews of Workhorse: reduce ubi8 size by relocating chown... (gitlab-org/build/CNG!1065 - merged) and CNG gitlab-shell: remove excess & Ruby (v2) (gitlab-org/build/CNG!1062 - merged), there are some inconsistencies across our multi-stage builds.

We should be using the same names for layers and intermediate stages and ensuring that we follow the same nomenclatures.

This is a separate concern from Proposal: CNG: standardize on `install` versus ... (#2392 - moved) which deals with container build directives.

Deliverables

1. Identify all multi-stage layers and the current names
2. Identify any other inconsistencies in our multi-stage processes
3. Document other inconsistencies, or fix them, depending on the broadness of the scope during discovery
4. Submit a merge request to standardize all of the layer names