Spike: See if we can write a guide for i.e. connecting to zookeeper that is also a test

[fhennig]

It's a problem that the CRs in the documentation can go out of sync over time, and the more we document the more it will become difficult to maintain.

For guides on specific aspects of the product, it would be good to embed manifest files from outside the documentation that are also simultaneously integrated into a kuttl test (or similar), so there's one test per guide and the test will make sure the guide still works.

A first try could also be done without our templating mechanism, so it's easier to integrate. With templating would be super fancy, if we also had tab blocks (#208) we could have multiple variants of a guide with different underlying files. But that sounds like it should be done in an additional iteration.

[fhennig]

We did this, the getting started tests are also testable #237