Provide more RBAC configuration examples which demonstrate how you can replace hierarchical structure with a flat designed one

[tjerman]

Since Corteza doesn't support hierarchical roles, we need to represent them in a flat structure.
Often, people come from systems with role hierarchy, so they expect us to also have it or are not sure how to rework their hierarchy into a flat structure.

• define a few examples, preferably simple and condensed, to demonstrate a specific scenario
• proof of concept on a Corteza instance
• document

[tjerman]

ref #314