Backend: add mermaid support to markdown parsing

[FrolickingMustelid]

We have to convert between

```mermaid
    graph TD 
        A[Client] --> B[Load Balancer] 
        B --> C[Server01] 
        B --> D[Server02]
```

and

<pre class="mermaid">
      graph TD 
        A[Client] --> B[Load Balancer] 
        B --> C[Server01] 
        B --> D[Server02]
</pre>

https://mermaid.js.org/intro/n00b-gettingStarted.html#_3-calling-the-javascript-api