doc: Add showcase on behavior tree testing

[arbimo]

• doc: add initial showcase draft for behavior tree testing
• doc: mainly cosmetic changes to showcase behavior-tree-testing

[arbimo]

@uwe-koeckemann @madmage Could you double check this? In particular, I believe the problem encoder part should be completed, but there are probably several minor improvements to be done.

[arbimo]

@uwe-koeckemann Could you handle the small todo above ?

[uwe-koeckemann]

@uwe-koeckemann Could you handle the small todo above ?

Done!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a4b433c) 84.92% compared to head (2bdf3cc) 84.92%.
Report is 44 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #539   +/-   ##
=======================================
  Coverage   84.92%   84.92%           
=======================================
  Files         200      200           
  Lines       26385    26385           
=======================================
  Hits        22408    22408           
  Misses       3977     3977           

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[arbimo]

Perfect, thanks!