Move curl-setopt constants to their own variablelist (#3586)

* Move curl-setopt constants to their own variablelist

* Make markup DocBook 5.2 compliant

Remove para and simpara elements from within the para element of constants' lisitem element (description)

* Remove related constant descriptions from within CURLOPT constant descriptions.

* Remove duplicate version availablity information and update the wording of some of them

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Co-authored-by: haszi <[email protected]>

Author: haszi