Add mermaid extension to wiki

[alexgarel]

This would enable making cool small graph on the wiki.

I use it in the infrastructure documentation, it's handy, really (also thanks to online editor)

[CharlesNepote]

I have already done it since months:

• https://wiki.openfoodfacts.org/Special:Version
• https://wiki.openfoodfacts.org/Test

Unfortunately, the mind maps don't allow links.

Are you sure we need to keep this? Can you give examples?

[alexgarel]

@CharlesNepote it's to do small diagrams, like explaining an onboarding pipeline.