Currently slack integration with zabbix 5.0 does not work.

This is due to a misconfigured api endpoint

Steps to reproduce:

1. https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/media/slack/media_slack.xml#475
2. var slack_endpoint = 'https://slack.com/api/'
3. http post https://slack.com/api Content-Type:'application/json; charset=utf-8' Authorization:'Bearer xoxb-.....'
   HTTP/1.1 301 Moved Permanently
   content-length: 229

1. url needs to be https://api.slack.com/
2. and or overridable with a macro please

Also please note: https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/templates/media/slack/media_slack.xml#494

Mattermost when calling slack

Result:
See screenshot...

Expected:
Working slack integration

Also nothing shows in the logs about this error