documentation

Pull request #2127: feature/ZBXNEXT-9533-7.2-D. environment variables in configuration files.

Merge in WEB/documentation from feature/ZBXNEXT-9533-7.2-D to release/7.2

* commit '5c8a7f77ef83197d73409675ec04522c6b344fae':
  [ZBXNEXT-9533] environment variables in configuration files (removed "What's new" example)
  [ZBXNEXT-9533] environment variables in configuration files (updated wording)
  [ZBXNEXT-9533] environment variables in configuration files (updated "What's new" wording)
  [ZBXNEXT-9533] environment variables in configuration files (refined page)
  [ZBXNEXT-9533] fixed docker-related links
  [ZBXNEXT-9533] environment variables in configuration files (refined page)
  [ZBXNEXT-9533] environment variables in configuration files (moved content)
  [ZBXNEXT-9533] environment variables in configuration files (updated wording)
  [ZBXNEXT-9533] environment variables in configuration files (updated examples)
  [ZBXNEXT-9533] environment variables in configuration files (updated wording)
  [ZBXNEXT-9533] environment variables in configuration files