Merge topic 'inst-doc-commands'

a312f190de Help/instrumentation: Restore custom target documentation
3a72d17df8 Help/instrumentation: Provide links to supporting pages
39b38fb047 Help/instrumentation: Clarify `postCTest` hook behavior
4174d2ab60 Help/instrumentation: Reflow to 80 columns

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !11553