documentation

Pull request #2322: feature/ZBX-22952-7.3-D. Authorization header forwarding; case-insensitive API headers.

Merge in WEB/documentation from feature/ZBX-22952-7.3-D to release/7.4

* commit 'b4fbdf57f7b0e14cdbc85b8fc62337c393e9cb16':
  [ZBX-22952] case-insensitive API headers
  [ZBX-22952] expanded Apache & NGINX instructions
  [ZBX-22952] minor wording update
  [ZBX-22952] Authorization header forwarding