Denotes one policy tag in a taxonomy (e.g. ssn). Policy
Tags can be defined in a hierarchy. For example, consider the following
hierarchy: Geolocation -> (LatLong, City, ZipCode). PolicyTag
"Geolocation" contains three child policy tags: "LatLong", "City", and
"ZipCode".
Required. User defined name of this policy tag. It must: be
unique within the parent taxonomy; contain only unicode
letters, numbers, underscores, dashes and spaces; not start or
end with spaces; and be at most 200 bytes long when encoded in
UTF-8.
Resource name of this policy tag's parent policy tag (e.g. for
the "LatLong" policy tag in the example above, this field
contains the resource name of the "Geolocation" policy tag).
If empty, it means this policy tag is a top level policy tag
(e.g. this field is empty for the "Geolocation" policy tag in
the example above). If not set, defaults to an empty string.