Values:
STATE_UNSPECIFIED (0):
Default value.
NOT_STARTED (1):
Backfill job was never started for the stream
object (stream has backfill strategy defined as
manual or object was explicitly excluded from
automatic backfill).
PENDING (2):
Backfill job will start pending available
resources.
ACTIVE (3):
Backfill job is running.
STOPPED (4):
Backfill job stopped (next job run will start
from beginning).
FAILED (5):
Backfill job failed (due to an error).
COMPLETED (6):
Backfill completed successfully.
UNSUPPORTED (7):
Backfill job failed since the table structure
is currently unsupported for backfill.
