Add the Postgres exporter to Kubernetes for CustomersDot - Staging only

Related to https://gitlab.com/gitlab-com/gl-infra/customersdot-ansible/-/issues/127

This MR is extracted from this other MR. It adds Postgresql exporter to Kubernetes for Customersdot.

Like the blackbox exporter, this exporter is made available as a chart in the prometheus-community/helm-charts project, already used in the Gitlab Helmfiles for monitoring.

Chart values

helm show values prometheus-community/prometheus-postgres-exporter > prometheus-postgres-exporter

Example values for prometheus-postgres-exporter chart

Manual tests

As both exporters were tested at the same time, you can check out test results in the original MR.

How to get CustomersDot staging database passwords

• Clone to this (private) project and cd into it
• Run ansible-vault edit --vault-id stg@prompt group_vars/stg/vault.yml
• You'll find the password to decrypt the vault in 1Password (1Password vault: Subscription portal - Name: CustomersDot Ansible - Staging vault)
• In the Staging vault, the db password is the value of vault_postgresql_db_password.