Get alerts from Prometheus Alertmanager via webhooks
Errbot Webserver plugin has to be configured first.
Configuration of this plugin is done using the webhook itself: /alerrt/<recipient>/<server>/
Add URLs like this to your Alertmanager webhook_configs:
MUC: "http://your.errbot.host:3141/alerrt/roomname/conference.jabberserver.org"
Direct message: "http://your.errbot.host:3141/alerrt/username/jabberserver.org"