Kroki filter is not invoked for non-markdown/asciidoc formats

Update: What's going on here is that we are not using the Kroki filter in the pipeline that handles non-markdown/asciidoc formats such as restructedText.

Summary

Seems like some diagrams are not send to the plantuml part of kroki. E.g. uml

Steps to reproduce

1. Setup kroki

2. Disable plantuml

3. Create a new project with a README.rst and this content

    .. uml::
        :caption:
   
        |CICD job|
        start
        :fetch git repo;
        :use job cache;
        :before script;
        |general preparation|
        :(un)set proxy settings;
        :echo debug information;
        :prepare ssh connection to CSC;
        :clone git dependency;
        |CICD job|
        :prepare script;
        |specific preparation e.g. Terraform|
        :prepare ci folder & set first environment vars;
        :prepare terraform variables;
        :prepare tagging;
        :prepare remote state;
        :initiate terraform state & modules;
        |CICD job|
        :execute job specific tasks;
        :update cache;
        stop

4. Notice how it doesn't render the UML correct

5. This works when having plantuml enabled

Example Project

What is the current bug behavior?

The diagram should be rendered the same way as with plantuml enabled.

Instead the diagram is not rendered at all with plantuml disabled.

Possible fixes

Workaround: Add your kroki plantuml endpoint in the plantuml section and keep both enabled:

e.g. `https://your-kroki-instance/plantuml/

@bufferoverflow @dlouzan @ercan.ucan