Add support for ZenUML (Mermaid)

[Pyroseza]

Add support for ZenUML (Mermaid)

See https://mermaid.js.org/syntax/zenuml.html

Available since 10.2.3

Example from docs

zenuml
    title Demo
    Alice->John: Hello John, how are you?
    John->Alice: Great!
    Alice->John: See you later!

Current error as seen in Joplin

[nils-a]

Using ZenUML seems to be dependent on @mermaid-js/mermaid-zenuml, too.

The current Joplin renderer is using mermaid 10.6.1 but still ZenUML does not render. Would it be "good" to change this here, so the editor renders the diagram while the renderer will not render it?