use of kroki server

[rdmueller]

kroki.io is a great way to render diagrams without different dependencies for each library.
It would be great if we could config docToolchain to use a (private) kroki server.

The way to go seems to be a ruby extension. Here are some link which should help to get this started:

ggrossetie/asciidoctor-intellij-plugin@ff452bb
https://blog.mrhaki.com/2016/11/awesome-asciidoctor-using-ruby.html
https://rubygems.org/gems/asciidoctor-kroki

The challenge will be to get this

• configurable. Default should be off. Even when configured, no public kroki server should be the fedault in order to keep data private
• working with generateHTML
• working with jBake