Zabbix

A......... [ZBX-18788] fixed webhook parameters not being reset on media type change

Merge in ZBX/zabbix from feature/ZBX-18788-5.0 to release/5.0

* commit 'c31b22c59e1a67844aa81286a9e9a44f00a0c035':
  A......... [ZBX-18788] removed unused code, on mediatype type change mediatypeid will be added to webhook_params therefor no need to check for it existence
  .......... [ZBX-18788] added changelog
  A......... [ZBX-18788] remove media type parameters on media type type field change from webhook