kroki.io unreliable, API 404 doesn't stop build

[fhennig]

1. The API outages of kroki.io which we use to render a few excalidraw diagrams are getting more.
2. Getting a 404 on the render API doesn't stop the build from going live

This isn't good, because now it happens that unrendered json text gets put where the diagram should be. This is the main page where excalidraw rendering is used: https://docs.stackable.tech/home/stable/concepts/s3.html (note that this page exists in multiple releases).

Acceptance criteria

• all usage of in-build excalidraw rendering is removed and replaced with editable draw.io SVGs. This needs to be done in all release branches!

[fhennig]

We just need to redraw the 3 images on the S3 page. It'll be more consistent that way anyways