Generate API Reference for CRDs

This issue includes the following tasks:

• Update our CRD OpenAPI Schema to provide all relevant information required for the docs (probably this is mainly the field description (+ potential examples?)) -- Done with !169 (merged)
• Generate markdown from the Schema using crdoc
  • Identify current limitations of crdoc for our CRDs if any -- All problems solved
  • Find out whether "real" markdown tables can be generated instead of html (@she)
• Add generated markdown to docs folder -- Done with !169 (merged), improved with !164 (merged)