documentation

Pull request #2390: Feature/ZBX-25639 7.3 D

Merge in WEB/documentation from feature/ZBX-25639-7.3-D to release/7.4

* commit '3e9e02b1068b3fadd214f646fd8ae847f45f4fe7':
  ZBX-25639 changed "Zabbix UI upgrade" to "Zabbix upgrade".
  ZBX-25639 improvements in consistency and clarity.
  ZBX-25639 improvements in consistency and clarity.
  ZBX-25639 changes in description of selected parameters.