Add documentation to qualify the comments on 'Anti-patterns' in module design

We should describe or document a design decision with rationale and reasoning on our module design, assuring we address the 'anti-pattern' comment on:

> Paraphrasing
> A module should never only deploy a single resource.

We should describe how our modules are rigged to deploy a single parent resource + its extensions, and tightly connected resources.

Document reasons we have single "resource" declarations in separate bicep files:
- [x] Deploy multiple instances via loops (nested loops)
- [x] Deployments happen on a different scope

Suggestions to where this doc could be:
- [ ] an FAQ page
- [x] the module design page