documentation

Pull request #3124: feature/ZBX-26754-7.5-D-exp. "Proxy load balancing and high availability" page improvement.

Merge in WEB/documentation from feature/ZBX-26754-7.5-D-exp to release/8.0

* commit 'fb01cf609d6aa2212be089676f898468e6a6b996':
  [ZBX-26754] removed <br>
  [ZBX-26754] temporarily removed task-related documentation
  [ZBX-26754] emphasized important step for configuring proxy load balancing; minor wording change
  [ZBX-26754] added helpful link to "Monitored by" host configuration parameter
  [ZBX-26754] clarified "Failover period" meaning & behavior; unified same parameter description between pages
  [ZBX-26754] fixed blockID
  [ZBX-26754] proxy load balancing/high availability: it's possible to set ServerActive to Zabbix server address
  [ZBX-26754] "Proxy load balancing and high availability" page improvement