documentation

Pull request #2750: ZBX-9370 Remember for 30 days option documented.

Merge in WEB/documentation from feature/ZBX-9370-7.3-D to release/7.4

* commit 'f41475820372c1386b121cb1ce9c07808a751fd2':
  ZBX-9370 removed mentions of persistent cookie.
  ZBX-9370 Remember for 30 days option documented.