Add support of mermaid diagrams

[iShift]

trafficstars

Describe the problem to be solved Support of the diagrams in the markdown

Describe the solution you'd like Add support of the mermaid

[adamaltman]

@iShift Mermaid is very heavy. We have it supported in our premium developer portal product, but I don't think it will be a good addition here because of the vast amount of dependencies required to support it.

[AlexVarchuk]

duplicate https://github.com/Redocly/redoc/issues/1459