[terraform] Change alarm names to reflect staging or production environment

Summary:
It's not readily apparent if the alarm occurs on staging or production. This alarm renames our alarms with "Staging" or "Production" prefixes.

Addresses https://linear.app/comm/issue/ENG-8157/investigate-adding-a-prod-staging-label-to-our-cloudwatch-alarm-emails.

Test Plan: terraform apply

Reviewers: bartek, varun

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12550