documentation

Pull request #1045: feature/ZBXNEXT-8357-6.0-D: Proxy history housekeeping limit removed.

Merge in WEB/documentation from feature/ZBXNEXT-8357-6.0-D to release/6.0

* commit 'ee0dcbf879644de54c9dc533afe663b95c8dd9a0':
  [ZBXNEXT-8357] Additional info on proxy history housekeeping limit removed
  [ZBXNEXT-8357] Updated grammar
  [ZBXNEXT-8357] Proxy history housekeeping limit removed