### 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/main/java/org/elasticsearch/xpack/core/DataTiersUsageTransportAction.java
*/
    private static void aggregateDataTierIndexStats(
        NodeStats nodeStats,
        RoutingNodes routingNodes,
        Map<String, String> indexByTier,
        Map<String, TierStatsAccumulator> accumulators
    ) {
        final RoutingNode node = routingNodes.node(nodeStats.getNode().getId());
        if (node != null) {
            StreamSupport.stream(node.spliterator(), false)
                .map(ShardRouting::index)
                .distinct()
                .forEach(index -> classifyIndexAndCollectStats(index, nodeStats, indexByTier, node, accumulators));
        }
    }
    /**
     * Determine which tier an index belongs in, then accumulate its stats into that tier's stats.
     */
    private static void classifyIndexAndCollectStats(
        Index index,
        NodeStats nodeStats,
        Map<String, String> indexByTier,
        RoutingNode node,
        Map<String, TierStatsAccumulator> accumulators
    ) {
        
        String indexTier = indexByTier.get(index.getName());
        if (indexTier != null) {
            final TierStatsAccumulator accumulator = accumulators.computeIfAbsent(indexTier, k -> new TierStatsAccumulator());
            accumulator.indexNames.add(index.getName());