Values:
TYPE_UNSPECIFIED (0):
Backup Type is unknown.
ON_DEMAND (1):
ON_DEMAND backups that were triggered by the customer (e.g.,
not AUTOMATED).
AUTOMATED (2):
AUTOMATED backups triggered by the automated
backups scheduler pursuant to an automated
backup policy.
CONTINUOUS (3):
CONTINUOUS backups triggered by the automated
backups scheduler due to a continuous backup
policy.
