Migrate away from bitnami/postgresql

[mgruner]

Reason: #353

Idea

• Use https://artifacthub.io/packages/helm/cloudnative-pg/cloudnative-pg, requires operator installation
• Use https://artifacthub.io/packages/helm/cloudpirates-postgres/postgres, no operator required

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[mgruner]

Maybe a less complex alternative: https://artifacthub.io/packages/helm/cloudpirates-postgres/postgres