v0.80.0

Changed

• PagerDuty incident titles now carry the description of the first firing alert (<cluster> - <AlertName>: <description>, plus the number of firing alerts when there is more than one), so the Slack incident card and push notifications show what is wrong instead of only the alert name.
• The Triggered via link on the PagerDuty Slack card points to the alert in Grafana instead of Alertmanager's relative external URL, which Slack could not render as a link.