OptionalnextOpaque continuation token. Pass as page_token to continue, even if this
response contains fewer than page_size pages or no pages. An absent or
empty token means there are no more results.
OptionalpagesThe requested pages. Each page includes only name, display_name,
domain, state, and update_time. Use GetPage for the full resource.
The list can be empty even when next_page_token is present.
Response for ListPages.