test (e2e/cli): use `max_items` instead of `max` when retrieving blog items: RSM `max` alone will return first (oldest) items, while `max_items` will return latest ones. As Libervia Pubsub as been fixed in this regard, tests are now fixed too.

these certificates are used for demo purpose only. Those must be the same as in
backend_e2e (they are generated there)