Add workflow and "project registry workflow" to the package docs

Background

During the Package team Think BIG meeting (see 2019-12-04), it was identified that there is a way to utilize existing package features in ways that provide some freedom in publishing packages to the GitLab registry that users may not be aware of. The behavior of being able to upload multiple unrelated packages to a single project provides users with an option if they do not want packages to be stored where the code is stored, or if there are specific ways they would like to organize their packages.

Proposal

Add a section to the package docs describing how this could be achieved (based on the previously recorded screencast: https://youtu.be/ui2nNBwN35c).

This doc is describing a possible workflow that users could utilize. A few other workflows have also been identified as possibly having value in being documented (MRs to come), so it makes sense to add a Workflow section to the package docs somewhere for users to reference.