add server side mermaid generation

[cyrilou242]

the mermaid library takes a lot of time to load. we should allow generation server-side, similar to latex server side generation.

• also maybe there are some script loading quickwins to optimize load time

Problem is the mermaid library does not have server side support yet: https://github.com/mermaid-js/mermaid/issues/3650

another option is to use a headless browser or mermaid cli directly: https://github.com/mermaidjs/mermaid.cli

[cyrilou242]

closing. now pre-generated with a headless browser See c5afc1b73e8f7979cfb64b185170f6322c55c285