Offer an option to ignore the file permissions check when calling the DB backup webhook

[KevinVitale]

As a consequence of putting in place a backup and recovery plan, I recently adopted the database backup webhook that is recommended by the team. However, Prysm is forcing me to use 0700 on --db-backup-output-dir, which my backup daemon can't access. I'd like to ask for a user override, which can disable the file permission check.