DocumentDB dbtype support

[P-Louw]

DocumentDB is a postgrsql based db used for cosmosdb with mongodb and postgresql query support. Earlier this year it went open-source and I am currently using it for a work project where we rollout documentdb with cnpg.

All in all a good replacement for mongodb with various supporters and users.

Adding DocumetnDB to support mongodb workloads changes:

• Add 'documentdb' database type to values.yaml
• Configure DocumentDB image (ghcr.io/ferretdb/postgres-documentdb)
• Add extensions: documentdb, pg_cron
• Configure shared_preload_libraries
• Support various ferretdb auth methods

Tests:

• Extension installation validation
• MongoDB client connectivity via mongosh
• CRUD operations with BSON data types
• Backup/restore and PITR functionality