feat: add mermaid support in codeblock

[C1C0]

Motivation

MermaidJS is a user-friendly diagramming tool. It is known for making diagram creation easier and faster than writing detailed descriptions. By adding MermaidJS to Memos, I aim to enable users to include various types of diagrams, like mind maps, in their notes. This integration is intended to make the sharing of complex ideas more straightforward and visually appealing, helping to communicate information more effectively in memos.

Example:

[MehadND]

What about the pricing? Free? Kind of confused. Thanks