private void releaseResources() {
        Utils.closeQuietly(backingStore != null ? backingStore::stop : null, "backing store for previous Checkpoints");
        Utils.closeQuietly(cpAdmin, "admin client for previous Checkpoints");
        cpAdmin = null;
        backingStore = null;
    }
Reads once the Kafka log for checkpoints and populates a map of
checkpoints per consumer group.

The Kafka log is closed after the initial load and only the in memory map is
used after start.
connect/mirror/src/main/java/org/apache/kafka/connect/mirror/CheckpointStore.java