CTest: document variables used to configure the Dart file
Currently the only place where some of the variables are documented are in the ctest(1) page, however these should really be listed on the CTest module's page.
I have noticed that on the internet people are referring to variables that are unknown to CMake such as
CMAKE_MEMORYCHECK_COMMAND, which is obviously wrong. I think the lack of documentation is what causes so much misinformation.
I propose documenting these variables directly on the CTest module's page and the mentions of the few that are present in ctest(1) just link to the CTest module's page with an anchor to the variable.
If this proposal looks good, then I can make a MR for it.