Any way to set global mermaid chunk options?

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/7279

^{Originally posted by cjdbarlow October 18, 2023}

Description

I would like to define chunk options for styling all mermaid diagrams created in the document, rather than having to manually do it each time. For example, I would like all graphs to use the stepBefore curve style. I can achieve this manually with:

```{mermaid}
%%{ init: { 'flowchart': { 'curve': 'stepBefore' } } }%%

graph_goes_here
```

But this distracts from the focus of the source document, which should be (imo) content rather than styling. I note similar things have been raised before so I am not sure if this is doable? Is there a way to prepend text to different code chunks?

Start by reading the linked discussions 7279 and 6209 to understand the proposed scope and prior answers. No implementation files or tests are named in the issue, so locate the existing Mermaid chunk handling and determine how document-wide options could be applied. Done means authors can set the curve style globally without repeating the Mermaid init block in each diagram.