Remove #alerts channel Alertmanager integrations

The #alerts channel in Slack is effectively /dev/null for notifications. We need to develop a plan for addressing alerts that are configured to spam this channel.

How do we?

• Determine which alerts can be safely removed?
• Determine which alerts should be directed elsewhere?
• Determine which alerts are captured with Service Metrics Catalogue?

Definition of Done

• The #alerts channel is silent from Alertmanager
• The #alerts channel is archived