Backup service: add option to delete backup from local server

[srosset81]

Backups can take a lot of space. Once they are copied to the remote server, there is usually no need to keep them in the local server. This could be done with a new setting on the BackupService.

⚠️ If the copy fails (for example if there is not enough space on the remote server), we should not delete the backup on the local server.