Zabbix

.........T [ZBXNEXT-5862] added Rocket.Chat media

Merge in ZBX/zabbix from feature/ZBXNEXT-5862-5.3 to master

* commit 'ba807da793e9c63b43564c2eb3418fc8aed01296':
  .........T [ZBXNEXT-5862] fixed after QA
  .........T [ZBXNEXT-5862] fixed readme after review
  .........T [ZBXNEXT-5862] fixed JS
  .........T [ZBXNEXT-5862] added missing trailing whitespace to readme
  .........T [ZBXNEXT-5862] added new prefix for field_ parameters and fixed typo
  .........T [ZBXNEXT-5862] added Rocket.Chat media