Support export mermaid diagrams to docx as images.

Title says it: I would like to export mermaid diagrams to docx as images.

![Image](https://github.com/user-attachments/assets/9c890088-ef18-4603-816b-0ae05bfbca20)

❯ myst -v
v1.3.26

## Proposal

## Additional notes

- maybe this helps
- https://www.npmjs.com/package/mermaid
- https://www.npmjs.com/package/markdown-mermaid-exporter
- https://www.npmjs.com/package/@mermaid-js/mermaid-cli