As visible at https://maintner.golang.org/logs, maintnerd currently serves only the latest growing mutation log fragment itself, and otherwise points maintner clients to fetch the frozen mutation log fragments from the golang-maintner-log GCS bucket directly. It relies on that bucket to have public access, a property we want to change as part of ensuring unintended data isn't accidentally publicly exposed.

Filing this to track updating maintner to serve the frozen mutation log fragments in a way that doesn't need that GCS bucket to stay publicly accessible.

CC @golang/release.