documentation

Pull request #2531: Feature/ZBX-25829 7.3 D

Merge in WEB/documentation from feature/ZBX-25829-7.3-D to release/7.4

* commit 'f1231d9c77686b27df01efadab2869e6eb90840e':
  clarified that indexed macros refer to problem events only (ZBX-25829)
  Improved Indexed macro section readability; clarified that indexes never refer to the recovery expressions (ZBX-25829)