cloudnative-pg
Support immutable versions
Pinning a specific version like http://ghcr.io/cloudnative-pg/postgresql:15.6-13 the contents of this manifest is changed every day. Good practice is that I am able to pin a version, that is really immutable. This means for every build there should be a new increasing additional version like 15.6-13-625 where 625 could be the number of the workflow run.
Normally, you should use a digest to pin a specific immutable version of the image, as outlined here: https://cloudnative-pg.io/documentation/current/quickstart/#part-3-deploy-a-postgresql-cluster
Starting with 1.23 you have more flexibility with image catalogs.
Regarding details about building the images, I will defer this to @NiccoloFei. We should increase the image version when there are significant changes in the combination of packages and libraries included in the image, but I don't have the exact details.
