ListUsableSubnetworksRequest requests the list of usable
subnetworks available to a user for creating clusters.
parent The parent project where subnetworks are usable. Specified
in the format ``projects/*``.
filter Filtering currently only supports equality on the
networkProjectId and must be in the form:
"networkProjectId=[PROJECTID]", where ``networkProjectId``
is the project which owns the listed subnetworks. This
defaults to the parent project ID.
page_size The max number of results per page that should be returned.
If the number of available results is larger than
``page_size``, a ``next_page_token`` is returned which can
be used to get the next page of results in subsequent
requests. Acceptable values are 0 to 500, inclusive.
page_token Specifies a page token to use. Set this to
the nextPageToken returned by previous list
requests to get the next page of results.