[META] Establish solid documentation

Status:
I worked over the docs during last weeks and I'm almost done. However, a few pages still need work - so adding todos for them.

todos:
* frontend: custom routes update
* community: ddd23 links + ddd23 page
* work over "getting started"
* add hosting options
* 📌 Document default components at website Active

Update on the todos:



* add hosting options
* #3479269: Document default components at website

New todo:
* Add a Drupal introduction page

I figured multi-frontend and redirect API responses were un-documented still also and quickly add pages for both. I guess we also should add some page below "Nuxt" for our varying starters.

Updated todos:
* #3490828: Add a Drupal introduction page
* Add page of "starters" below nuxt
* Add list of unified hosting companies

I created the list of unified hosting options: https://github.com/drunomics/lupus-decoupled-website/commit/4b86ecf35bfb...

What's left is only
* #3490828: Add a Drupal introduction page
* Add page of "starters" below nuxt
which each have a dedicated issue. Given that, I think we can the current state of the docs "solid", call this done and add those two pages in the mentioned issues as follow-up.