documentation

Pull request #1986: feature/ZBX-23664-6.4-D3. updated Agent interface availability behavior for active checks.

Merge in WEB/documentation from feature/ZBX-23664-6.4-D3 to release/6.4

* commit '5e2da72877f7e1796b44423c1fcd4ed899ad1426':
  [ZBX-23664] fixed links
  [ZBX-23664] updated Agent interface availability behavior for active checks
  [ZBX-23664] fixed "Yellow" availability icon conditions
  [ZBX-23664] updated Agent interface availability behavior for active checks
  [ZBX-23664] minor wording refinement
  [ZBX-23664] updated Agent interface availability behavior for active checks
  [ZBX-23664] updated Agent interface availability behavior for active checks
  [ZBX-23664] improved host availability description/readability