Inline adoc files when they are included exactly once.
Also fix language tags because this inlining gives us better information
on what language the code is written in.
* Create rule S6412
* init s6412
* fixes after review
* remove one ask yourself question
* Add code highlighted tag to code example
Co-authored-by: eric-therond-sonarsource <eric-therond-sonarsource@users.noreply.github.com>
Co-authored-by: eric-therond-sonarsource <eric.therond@sonarsource.com>
Co-authored-by: Nils Werner <nils.werner@sonarsource.com>
