Post high-urgency PagerDuty incidents to Slack

When something breaks, everyone should see it in the same place. Whenever a high-urgency incident opens in PagerDuty, this posts it to the Slack channel you choose with the service, who is on call right now and a link straight to the incident.

Low-urgency incidents are left out.

PagerDutyWhen an incident is opened. Save it as incident.When an incident is opened. Save it as incident.

Post the incident to #incidentsSend message to channel. Save it as posted.:rotating_light: *High-urgency incident #incident.incident_number: incident.title* *Service:* incident.service_name *On call:* incident.on_call <incident.html_url|Open the incident in PagerDuty>Slack