Code describes the status of the operation (or one of its
steps).
Values:
STATUS_UNSPECIFIED (0):
Unspecifed code.
DONE (1):
The operation or step has completed without
errors.
NOT_STARTED (2):
The operation or step has not started yet.
IN_PROGRESS (3):
The operation or step is in progress.
FAILED (4):
The operation or step has completed with
errors. If the operation is rollbackable, the
rollback completed with errors too.
CANCELLED (5):
The operation or step has completed with
cancellation.
