placeBlockInDefaultTheme config action: add documentation and tests for applying block settings

Moving to the recipes initiative project where the documentation lives.

Moving it back because the test coverage would need to go into core.

In Drupal core changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to the Core change policies → . Also mentioned on the version → section of the list of issue fields documentation.

Thanks for the explanation, I will try to be more cognizant of that in the future.