Values:
INDEXING_STATUS_UNSPECIFIED (0):
Defaults to SUCCEEDED.
PENDING (1):
The target site is in the update queue and
will be picked up by indexing pipeline.
FAILED (2):
The target site fails to be indexed.
SUCCEEDED (3):
The target site has been indexed.
DELETING (4):
The previously indexed target site has been
marked to be deleted. This is a transitioning
state which will resulted in either:
1. target site deleted if unindexing is
successful;
2. state reverts to SUCCEEDED if the unindexing
fails.