argocd-apps docs

Operational notes for the manifests in this repo.

Doc	What it covers
cnpg-backups.md	How CNPG Postgres backups (WAL archiving + nightly base backups) to Ceph RGW are configured.
cnpg-restore.md	Restoring a CNPG cluster: full recovery, point-in-time recovery, cutover, and gotchas.