The Cloud Storage url of the file(s) to scan, in the format
gs://<bucket>/<path>. Trailing wildcard in the path is
allowed. If the url ends in a trailing slash, the bucket or
directory represented by the url will be scanned non-
recursively (content in sub-directories will not be scanned).
This means that gs://mybucket/ is equivalent to
gs://mybucket/*, and gs://mybucket/directory/ is
equivalent to gs://mybucket/directory/*. Exactly one of
url or regex_file_set must be set.
