Custom Templates

[crooks]

Motivation
The Alertmanager messages displayed in Mattermost each take up a lot of screen space. I'd like to be able to customize the message so it provides a short summary, something like:
alertname=InstanceDown, instance=hostname, severity=warning
If colour could be use to denote Firing or Resolved, that would be ideal.

Feature
Ability to customize the output format of generated Mattermost messages. The Slack integration appears to include options for customized Go templates but I don't think this can be done with the webhook_config integration.

Additional context
The following blog post provides some examples of custom templates but I don't see a way to integrate these with the webhook_config.
https://prometheus.io/blog/2016/03/03/custom-alertmanager-templates/

[jangrewe]

I would love to see this, too. Right now push notifications only tell me there was a message from a webhook in a channel, but not any of the contents. At least a header line with the summary would be nice.

[cpanato]

sounds a nice addition, are you willing to open a pr to add that?