documentation

Pull request #2886: Feature/ZBXNEXT-8698 7.3 D

Merge in WEB/documentation from feature/ZBXNEXT-8698-7.3-D to release/7.4

* commit 'd16aaa3c13236ccfd8892973660b5b0bef89fe2f':
  ZBXNEXT-8698 removed redundant sentence.
  ZBXNEXT-8698 changed a command.
  ZBXNEXY-8698 made minor adjustments.
  ZBXNEXT-8698 reformatting and improvements.
  ZBXNEXT-8698 fixed parameter names.
  ZBXNEXT-8698 moved and expanded a section.
  ZBXNEXT-8698 various fixes.
  ZBXNEXT-8698 fixed formatting, added a note.
  ZBXNEXT-8698 formatting and wording improvements.
  ZBXNEXT-8698 added information about frontend to server encryption.
  ZBXNEXT-8698 added parameters, updated frontend installation instructions.
  ZBXNEXT-8698 added new parameters.