There are two basic configurations for pg_statsinfo in warm-standby.
pg_statsinfo will run even on the standby server and parse server logs written in standby. However, it doesn't take any snapshots because the standby server doesn't accept connections.
You can put the repository to the third server independing from the active and the standby servers. This configuration enables to access the same repository always no matter which server is the active.
If you don't have no more servers other than the active and the standby servers, you can put the repositories together with them. Snapshot from the active server will be stored in the server. On the other hand, the standby server cannot store any statistics, but it will not a problem because there are no checkpoints nor autovacuums in the standby server.
Since snapshots for the active server will be also replicated, you can analyze the snapshots after failover from the previously-standby server (in active then).