Alerting: Fix integration key so it's stored encrypted for Pagerduty notifier (#27484)
Alerting: Fix integration key so it's stored encrypted for Pagerduty notifier (#27484)

Fixes an issue introduced by migration in #25980 which 
removed storing the Pagerduty integrating key encrypted.
grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana