documentation

[ZBXNEXT-8887] updated drule API documentation

Merge in WEB/documentation from feature/ZBXNEXT-8887-7.0-API to release/7.0

* commit 'd2bfd5ee96424dbebaadb2dee226a7aea4826a60':
  [ZBXNEXT-8887] added error parameter to drule object; updated drule.get method