Add Kroki renderer

[rlanyi]

This pull request adds support for https://kroki.io/ that can be used to generate diagrams from many different kinds of formats. It can be used as a replacement of the already existing PlantUML renderer and many other formats like GraphViz, Nomnoml, Mermaid and others.

The implementation is based on the PlantUML renderer. There's an important difference in the way it can be used: in the first line of the diagram definition the selected format must be entered.

Markdown Example 1:

```kroki
mermaid
graph TD
  A[ Anyone ] -->|Can help | B( Go to github.com/yuzutech/kroki )
  B --> C{ How to contribute? }
  C --> D[ Reporting bugs ]
  C --> E[ Sharing ideas ]
  C --> F[ Advocating ]
```

Markdown Example 2:

```kroki
plantuml
skinparam monochrome true
skinparam ranksep 20
skinparam dpi 150
skinparam arrowThickness 0.7
skinparam packageTitleAlignment left
skinparam usecaseBorderThickness 0.4
skinparam defaultFontSize 12
skinparam rectangleBorderThickness 1

rectangle "Main" {
  (main.view)
  (singleton)
}
rectangle "Base" {
  (base.component)
  (component)
  (model)
}
rectangle "<b>main.ts</b>" as main_ts

(component) ..> (base.component)
main_ts ==> (main.view)
(main.view) --> (component)
(main.view) ...> (singleton)
(singleton) ---> (model)
```

[NGPixel]

Thanks! Just make sure your PRs are against the master branch next time, not latest.

[kbfifi]

I'm excited to see so much support for text generated diagrams! Will it be possible to to configure WikiJS so that one can use a self managed Kroki docker-compose server as described here?

[NGPixel]

@kbfifi Yes, you can define the server URL you want to use.

[elmorejd]

@kbfifi would you update Mermaid from 8.8.2 to the latest 10.7 or close to?
https://github.com/mermaid-js/mermaid
Would really appreciate it!