documentation

Pull request #1798: feature/ZBXNEXT-9155-7.0-D. Improved usability of "Override host" field in configuration form for "Item value" and "Gauge" widgets.

Merge in WEB/documentation from feature/ZBXNEXT-9155-7.0-D to release/7.0

* commit 'd26d8106a29418408247c9e16521993eab4d39a8':
  updated outdated configuration form screenshot for "URL" widget
  [ZBXNEXT-9155] improved usability of "Override host" field in configuration form for "Item value" and "Gauge" widgets