Support Mermaid translation

[3y3]

Mermaid is first class citien feature for Diplodoc platform. So we should translate in from the box.

But it is hard to find translatable units here.

Nice to have some universal solution here. This solution should be written one time end works with all existed and future Mermaid diagrams.

At minimum we need some simple extendable solution, which works fine with existed diagrams for small code lines cost (2k lines at max). Extensibility should be implemented as declarative feature. For example - json schema over Mermaid parsed json AST.