Consider MermaidJS architecture diagram support

[ptgott]

We removed support for MermaidJS in the docs site in December 2023. Since then, MermaidJS has introduced a new diagram type, the architecture diagram, that is far more suited for our use case than the classic flowchart.

Because the architecture diagram does not include directionally sensitive rendering logic, like the flowchart does, and renders edges with neat right angles, it leads to more predictable relationships between text and the resulting architecture diagrams. (Flowcharts were not intended as architecture diagrams, after all.)

In addition, architecture diagrams support icons, both built-in and custom-made.

Let's consider allowing for architecture diagram support in the docs engine, including workflows for:

• Rendering diagrams
• Ensuring quality (e.g., don't allow flowcharts, only architecture diagrams)
• Styling diagrams for the Teleport brand