Provide the container registry DB by default for our built Postgresql chart

Summary

We can't guarantee that a fresh install is really a fresh install due to the nature of Backup/Restores. But we can make sure our chart always deploys a separate logical registry database.

Proposal

• DB, User and Extensions provisioning:
  • Use templates/initdb-configmap.yaml to create extra logical DBs, Users and extensions, as I can't find a way to provide DB/User initialization other than the auth: key of the Postgres Bitnamy chart, and it does not seem to support multiple DBs.
    • We would use IF NOT EXISTS to make it idempotent. But might not be critical as the Postgresql PV will persist the state file that indicates that we have already initialized it.
    • Delver further: https://github.com/bitnami/containers/blob/main/bitnami/postgresql/17/debian-12/rootfs/opt/bitnami/scripts/postgresql/setup.sh
    • All of this is only relevant if postgresql.install: true.
  • The global.psql.{main | ci} seem very much coupled to GitLab Rails implementation and configuration. I'm a bit reluctant to extend that. I believe the best approach is to expose global.registry.database to the templates/initdb-configmap.yaml to be able to initialize DB/User/Extensions.
  • We can merge the global into the local registry.database stuff. There's no real reason to deprecate the current configs.
  • Operator V2 relies on external DB anyway.
• Migrations and SKIP_POST_DEPLOYMENT_MIGRATIONS
  • Already supported
  • We won't support automated post deploy migrations.

Implementation details

• Provide new global.registry.database.{user, name} keys to the chart.
• Default there values to whatever the container registry team prefers.
• Within the registry chart templates functions, if registry.database.{user, name} is set, give preference to that, because it means that users have already configured that for an external instance. If it's not set, take the ones from global.
• On the templates/initdb-configmap.yaml file, create a new data.init_registry.sh key, which executes psql commands to create the registry user and database, taking their names from the new global keys.
• If certain DB extensions are required, also create them within the same script.

Relevant links

• Include a Default Database for the Container Re... (gitlab-org/gitlab#480742 - closed) • Hayley Swimelar • 17.8 • At risk
• Release container registry with metadata databa... (gitlab-org&5521) • Jaime Martinez, Hayley Swimelar+ • On track