Values:
STATE_UNSPECIFIED (0):
Default value. This value is unused.
STATE_ACTIVE (1):
This subscription is active and the data is
accessible.
STATE_STALE (2):
The data referenced by this subscription is
out of date and should be refreshed. This can
happen when a data provider adds or removes
datasets.
STATE_INACTIVE (3):
This subscription has been cancelled or
revoked and the data is no longer accessible.