Add easy way to create an backup instance of a schedule

[toabi]

Summary

As "cluster operator or developer"
I want "to quickly create a new backup off-schedule"
So that "I can run a upgrade or restore it somewhere else quickly"

Context

The Schedule objects are great to have backups in regular intervals.

But sometimes you want to have a backup now. E.g. before a cluster/app upgrade or when restoring the current state of a customer application in a local dev environment.

It would be cool to have something similar as with CronJob: kubectl create job test-job --from=cronjob/a-cronjob for Schedules.

Implementation Ideas

Maybe the Backup(https://k8up.io/k8up/2.8/how-tos/backup.html) could get a spec.backend.fromSchedule.name field where it then pulls all its info? That would be very minimal and save lots of copy-pasting that info.