Setup pagerduty for proper use

[yuvipanda]

In #2693, we've setup pagerduty to send us alerts from grafana. But we aren't using it to its full extent, and we should.

• [x] Make sure everyone has pagerduty accounts with access to the 'datahub' service that we send alerts to
• [ ] Adding alerts for 5xx errors
• [ ] Integrate pagerduty into slack so we get alerts into uctech (https://support.pagerduty.com/docs/slack-integration-guide