### Elasticsearch Version

8.1.2

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

ESS on Azure

### Problem Description

The `_xpack/usage` API reports the size of the data set per data tier. However, it uses the local disk size as the metric it reports on and this is 0 (zero) for partially mounted indices, hiding the size of the data set mounted on the frozen tier.

We should switch to using the `total_data_set_size` metric that was introduced when we added the frozen tier/partially mounted indices.

### Steps to Reproduce

Mount a partially mounted index on a dedicated frozen tier. Use the `_xpack/usage` API and see that no (or very little) data is reported on frozen tier.

### Logs (if relevant)

_No response_
x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/DataTiersUsageTransportActionTests.java
Map<Index, List<IndexShardStats>> indexStats = new HashMap<>();
            for (ShardRouting shardRouting : routingNode) {
                ShardId shardId = shardRouting.shardId();
                ShardStats shardStat = shardStat(bytesPerShard, docsPerShard, shardRouting);
                IndexShardStats shardStats = new IndexShardStats(shardId, new ShardStats[] { shardStat });
                indexStats.computeIfAbsent(shardId.getIndex(), k -> new ArrayList<>()).add(shardStats);
            }
            NodeIndicesStats nodeIndexStats = new NodeIndicesStats(new CommonStats(), indexStats);
            nodeStatsList.add(mockNodeStats(node, nodeIndexStats));
        }
        return nodeStatsList;
    }
    private static ShardStats shardStat(long byteCount, long docCount, ShardRouting routing) {
        StoreStats storeStats = new StoreStats(byteCount, 0L, 0L);
        DocsStats docsStats = new DocsStats(docCount, 0L, byteCount);
        CommonStats commonStats = new CommonStats(CommonStatsFlags.ALL);
        commonStats.getStore().add(storeStats);
        commonStats.getDocs().add(docsStats);
        Path fakePath = PathUtils.get("test/dir/" + routing.shardId().getIndex().getUUID() + "/" + routing.shardId().id());
        ShardPath fakeShardPath = new ShardPath(false, fakePath, fakePath, routing.shardId());
        return new ShardStats(routing, fakeShardPath, commonStats, null, null, null);
    }
    private static NodeStats mockNodeStats(DiscoveryNode node, NodeIndicesStats indexStats) {
        NodeStats stats = mock(NodeStats.class);
        when(stats.getNode()).thenReturn(node);
        when(stats.getIndices()).thenReturn(indexStats);
        return stats;
    }
}