feat(backup): add option validation for backup creation

[ChanYiLin]

ref: https://github.com/longhorn/longhorn/issues/7070

backupstore: If the backup has the option backupmodea: full, it will pretend there is no last backup, and backup all the blocks of the current volume.

longhorn-manager: We need to validate the option of the Backup to check if there is any typo in the option.