kroki integration

[achimgrimm]

It would be great to have the kroki server (https://kroki.io/) generate the context map diagram.
This would allow build workflows without the need to install Graphviz on the local system.

[stefan-ka]

Thanks for the input @achimgrimm! Great idea... Probably I will not have the time within the next weeks, but I'll definitely have a look at this one. Contributions are always welcome as well ;)