Merge topic 'env-init-configs'

ef56eefc9b cmake: Allow CMAKE_CONFIGURATION_TYPES to be set by environment variable
e216b9bbd3 cmake: Allow CMAKE_BUILD_TYPE to be set by environment variable
6986a382a9 Help: Document when CMAKE_BUILD_TYPE and CMAKE_CONFIGURATION_TYPES are set
e96169a3ec Help: Cross-reference CMAKE_CONFIGURATION_TYPES from CMAKE_BUILD_TYPE
03bd9c4c10 cmMakefile: Add helper to initialize CMAKE_CONFIGURATION_TYPES

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !6291