feat: Create a CNPG Extension Image and allow running the sidecar against an existing CNPG Cluster #315
Description
Image Volume Extensions are a feature that allow postgres extensions to be loaded into a CNPG Cluster without baking them into the core postgres image. I'd appreciate being able to use a DocumentDB extension image with the sidecar proxy in order to turn an existing CNPG Cluster into a mongodb-compatible database, since I have no need or desire to run an entire separate Postgres Cluster just for one or two applications that need a document db.
Extension Image examples: https://github.com/cloudnative-pg/postgres-extensions-containers