Add SLI monitoring for Praefect's Cloud SQL instance

This change adds service-level monitoring for Praefect's Cloud SQL instance.

It requires https://ops.gitlab.net/gitlab-cookbooks/chef-repo/-/merge_requests/4053, which imports more stackdriver metrics into Prometheus.

It adds the following items:

1. Request rate for Cloud SQL
2. Error rate for Cloud SQL
3. Tooling links to the Google Cloud Console dashboard

Component Level Indicators

(no data until recording rules are merged in)

Detailed Panels

These panels to not use the recording rules, so show how the graphs will look

Snapshot: https://dashboards.gitlab.net/dashboard/snapshot/enOXljCPlf9vTLrvT8fzOMXcNdpqU3bU