Add DocumentDB extension to CNPG image catalog and design catalog integration

[WentingWu666666]

Summary

Add the DocumentDB extension to the CloudNative-PG extension image catalog and design how the DocumentDB operator leverages CNPG image catalogs for extension management.

Motivation

Currently, the DocumentDB Kubernetes Operator bundles extensions directly into custom container images. CloudNative-PG provides an Image Catalog mechanism (catalog-extensions-trixie.yaml) that allows extensions to be declared and managed declaratively.

By adding the DocumentDB extension to the upstream CNPG artifacts catalog, we can:

• Allow users to consume DocumentDB extensions through the standard CNPG image catalog workflow
• Reduce custom image maintenance burden
• Improve compatibility with the broader CNPG ecosystem

Proposed Work

1. Upstream: Add DocumentDB extension to CNPG artifacts

• Submit a PR to cloudnative-pg/artifacts to add the DocumentDB extension entry to image-catalogs/catalog-extensions-trixie.yaml

2. Design: How the operator uses Image Catalogs

• Design how DocumentDB CR references or auto-configures CNPG ImageCatalog / ClusterImageCatalog resources
• Determine whether the operator should:
  • Create and manage ImageCatalog CRs automatically
  • Reference a user-provided catalog
  • Support both modes (auto-create with opt-out)
• Define the interaction between the operator's cluster provisioning and CNPG's image catalog selection
• Consider upgrade and version-pinning strategy for catalog images

Acceptance Criteria

• DocumentDB extension is added to the upstream CNPG extension catalog (Trixie)
• Design document describing how the operator integrates with CNPG image catalogs
• Operator changes implemented to leverage image catalogs for extension management

References

• CNPG Image Catalogs: https://cloudnative-pg.io/documentation/current/image_catalog/
• Target file: https://github.com/cloudnative-pg/artifacts/blob/main/image-catalogs/catalog-extensions-trixie.yaml
• Related: Clean up our image story #194 (Clean up our image story)

[WentingWu666666]

We could use https://github.com/xgerman/postgres-extensions-containers/tree/xgerman/documentdb

[WentingWu666666]

https://github.com/cloudnative-pg/postgres-extensions-containers/blob/main/CONTRIBUTING_NEW_EXTENSION.md