Make backup file names configurable

[kyrbrbik]

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. ghcr.io/zalando/postgres-operator:v1.14.0
• Where do you run it - cloud or metal? Kubernetes or OpenShift? [AWS K8s | GCP ... | Bare Metal K8s] Bare metal k8s
• Are you running Postgres Operator in production? [yes | no] Yes
• Type of issue? [Bug report, question, feature request, etc.] Feature request

When using logical-backups cronjob it would be useful to be able to change the backup file names from Unix time to something more human readable.

This could allow for better filtering of backups etc.

I propose adding a new env variable for the logical backups that would allow you to change the name generated from $(date +%s) to some other $(date) formats.

I have a PR for this ready that I'm gonna submit later today.