documentation

Pull request #4660: feature/ZBXNEXT-10707-7.5-D

Merge in WEB/documentation from feature/ZBXNEXT-10707-7.5-D to release/8.0

* commit '25e361119282b33784bb0f1c821bb99225a520a8':
  [ZBXNEXT-10707, ZBXNEXT-10347] mentioned ClickHouse Keeper; clarified meaning of "ClickHouse cluster"
  [ZBXNEXT-10707, ZBXNEXT-10347] added note on TTL; made link to ClickHouse docs as note
  [ZBXNEXT-10707, ZBXNEXT-10347] fixed command for applying TTL changes immediately
  [ZBXNEXT-10707, ZBXNEXT-10347] added ClickHouse cluster version
  [ZBXNEXT-10707, ZBXNEXT-10347] added instructions for configuring ClickHouse clusters