documentation

Pull request #3050: feature/ZBX-26442-7.0-D. Improved "Secure user for Zabbix agent" best practice (mentioned agent2 & proxy).

Merge in WEB/documentation from feature/ZBX-26442-7.0-D to release/7.0

* commit 'f0c03aa503427fe3c099d00fc331cd878d422253':
  [ZBX-26442] refined wording
  [ZBX-26442] refined formatting
  [ZBX-26442] improved "Secure user for Zabbix agent" best practice (mentioned agent2 & proxy)