Allow calling arbitrary URLs on success/failure for monitoring purposes

[belidzs]

I'm using a self-hosted version healthchecks.io to get notified if one of the configured webhooks are not called in a certain period (dead man's switch).

I could set up my previous backup solution to call this URL after the backup has successfully completed. If it had failed or hadn't even start, the URL was never called and I got an alert.

It would be nice if k8up was able to call an arbitrary URL on success. This should be configurable for each backup definition (i.e. separate URL for every PVC, PreBackupPod, k8up.io/backupcommand)

[belidzs]

Now that I think about it, a generic onSuccessCommand and onFailureCommand would be probably a better idea. These could be used to call cURL, send an email, etc.