These are registered in the store's metrics registry when the store rebalancer first calls into MMA, since we know the StoreID at that point, and the StoreID is needed as a key in the internal maps in MMA. This late registration may be the cause for them missing from metrics.yaml.

For comparison, admission control also has late registration of per store metrics, but it happens in topLevelServer.PreStart (see the call to SetPebbleMetricsProvider), so it is not as late. We could do something similar for MMA.

Epic CRDB-55052

Jira issue: CRDB-57911