Use kroki.io to render diagrams

[phertweck]

In context with #31, it would be good to use kroki.io to render diagrams. Especially to support a broader variety of diagram libraries.

[00Asgaroth00]

+1
It would be great if kroki was an option to use, but, to also make it configurable for using a local instance or and external instance (kroki.io)

I'm currently having an issue generating rackdiag images as the docker container does not appear to have rackdiag/rackdiag3 installed, according to the following message:

> Task :generateHTML
Converting /project/docs/rack_layout.adoc
rack_layout.adoc: line 27: Failed to generate image: Could not find the rackdiag, rackdiag3 executable in PATH; add it to the PATH or specify its location using the rackdiag document attribute

[rdmueller]

Yes, great idea! Anyone ready to create a pull request?

[phertweck]

Unfortunately, I don't have any idea how to configure docToolchain to use an external kroki instance.

[rdmueller]

https://docs-as-co.de/news/diagrams-with-kroki/

but it would be also great to have a kroki instance running inside the docker container. This should be possible with the fat-jar provided by kroki.io

[rdmueller]

see also docToolchain/docToolchain#531