[feature request] Add a custom resource to enhance query capabilities for backup results

Please, answer some short questions which should help us to understand your problem / question better?

• Which image of the operator are you using? e.g. registry.opensource.zalan.do/acid/postgres-operator:v1.9.0
• Where do you run it - cloud or metal? Kubernetes or OpenShift? [Bare Metal K8s]
• Are you running Postgres Operator in production? [yes]
• Type of issue? [feature request]

I would like to suggest improving the current functionality of the Postgres Operator. While it supports backups, creating a backup currently requires accessing the Postgres Pod and executing shell commands. The same goes for scheduled backups, which rely on using Linux's crontab. This approach is not user-friendly as users have to manually check the backup sets by executing "wal-g backup-list" command within the Pod, and examine the Pod's crontab for scheduled backups. Therefore, I propose adding a custom resource that tracks the execution status of backups. Users can easily query this resource to obtain information about backup sets. Additionally, the management of scheduled backups can be handled using Go's cron or Kubernetes' crontab, greatly improving the user experience.

Such as https://github.com/percona/percona-postgresql-operator/blob/main/pkg/apis/pg.percona.com/v2beta1/perconapgbackup_types.go

If there are no issues with this feature, I am willing to submit a PR to implement it.

Start by reviewing the current backup and scheduled-backup implementation in the operator, then compare its design with Percona's pkg/apis/pg.percona.com/v2beta1/perconapgbackup_types.go. Define the custom resource's backup status and queryable backup-set information, and determine how scheduling would replace Pod shell commands, wal-g backup-list, and Linux crontab; done requires a reviewed API and implementation plan.