[FEA] Add mermaid.js support

[msarahan]

Describe the solution you'd like

I want to be able to write Mermaid diagrams in our docs, similar to what we can do in Github.

@jameslamb found this guide, which seems simple enough, but I don't know if there are hidden dragons. https://stuff-things.net/2025/01/19/mermaid-diagramming-in-jekyll-in-2025/

Describe alternatives you've considered
Static images of diagrams created elsewhere. This is viable, but the perk of mermaid diagrams is that the source code of the diagram lives in the docs and can be fixed or improved in the future.

Additional context

• https://github.com/mermaid-js/mermaid
• https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-diagrams