send Alertmanager alerts to GitLab

It would be nice to have alerts show up in GitLab as issues so that work can be tracked alongside the rest of our kanban boards. The translation team has experimented with GitLab alerts and this serves as a good example of how that workflow could work if Alertmanager opens alerts in GitLab. TPA also uses incidents to track outages, so this would be a nice fit.

Typically, critical alerts would open alerts in GitLab and part of triage would require operators to make sure this queue is cleared up by the end of the week, or an incident created to handle the alert.

GitLab has a tool called helicopter to add notifications to issues when they reference a specific silence, repeatedly pinging operators for open issues, but we do not believe this is necessary.