Move static assets out of the `/docs` and `/docs-kits` directories

## Description

Docusaurus provides a special directory for static assets. See [the documentation](https://docusaurus.io/docs/static-assets).
This makes them easy to reference and could potentially also improve build performance, since they are just copied to the output dir during build.

We need to go through our "docs" directories, move every image, that is not yet place in the `/static` directory and adjust links.

While doing that, we should also introduce a proper folder structure. Currently it is quite overwhelming and hard to find stuff due to the flat structure