Feat/add certification process2

[garloff]

Explain SCS DigiSov and Certs. How to get into compliance.

- Explain the motivation for the SCS certification levels rooted in
  the levels of digital sovereignty.
- Give a practical example how to achieve the SCS certification by
  running the tests.
- Hints on how to get listed, why we have the HM there and how to
  react to failed runs.

[garloff]

Note that I have pushed the changes to the staging branch, so we should see the results in https://docs-staging.scs.community/ in a few minutes.

[garloff]

This one supercedes PR #251.

Please review the end results, I unfortunately went through some trial and error for getting docusaurus to do what I need.

Note that the Markdownlint check fails with or without this patch. It barfs on the generated index files, not sure whether the generation process can be tweaked or whether we'd need to filter things out for that check. In any case, that's unrelated to the contribution from this PR.

[garloff]

• From Compliant cloud environments overview to 'Compliant Clouds'

This page was called overview before and the document's name is still overview (and should stay so, as it is linked to from various places). That's why I kept the word "overview" in the title. A compromise could be 'Compliant Clouds overview' to keep the relation with the link name.

[garloff]

3. Move "The taxonomy of digital sovereignty" from Certification Overview Page

Starting with a short introduction and the list of scs certification levels helps engage visitors, reducing the chance of overwhelming with too much text at in the beginning. Introduction sentence could be:

Agreed. While I think we should explain how our understanding of digital sovereignty drives the levels of SCS certification, not everyone wants to read through it, so splitting out additional background info into a separate page makes sense.

[garloff]

I suggest to shorten the sidebar item texts to keep them one liners for better readability such as:

* From `Getting SCS-compatible certification (for operators)` to `Certification Process` or `Getting Certified`

* From `Example testing and adjustment for SCS IaaS-compatible compliance` to `Testing Compliance' or `Compliance Testing`

* From `Compliant cloud environments overview` to 'Compliant Clouds'

Do I need to change the titles in the pages? Or is there a straight-forward way to do it in sidebarStandards.js?