documentation

Pull request #1820: feature/ZBXNEXT-8316-7.0-D-API. Added Item history widget (API).

Merge in WEB/documentation from feature/ZBXNEXT-8316-7.0-D-API to release/7.0

* commit '2f07f19c9ab224051e0be4304904b29ae0125a29':
  [ZBX-24490] added missing task to changelog
  [ZBXNEXT-9193] parameter `sortfield` now supports `ns`
  [ZBXNEXT-8316, ZBXNEXT-9193, ZBX-24488] added Item history widget (API)