Build a prometheus alert based on the pending post-migrations
As part of &585 (closed), we need a way to alert release managers that post-migrations are piling up. For context, #2020 (closed) introduced some metrics to keep track of the pending migrations, this information is shown in the release manager dashboard.
Proposal
Create an alert in Prometheus that gets triggered after having more than 5
pending migrations on gprd, we get alerted in #f_upcoming_release
channel.