### 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
DiscoveryNodes.Builder discoBuilder = DiscoveryNodes.builder();
        DiscoveryNode leader = newNode(nodeId++, DiscoveryNodeRole.MASTER_ROLE);
        discoBuilder.add(leader);
        discoBuilder.masterNodeId(leader.getId());
        DiscoveryNode hotNode1 = newNode(nodeId++, DiscoveryNodeRole.DATA_HOT_NODE_ROLE);
        discoBuilder.add(hotNode1);
        DiscoveryNode hotNode2 = newNode(nodeId++, DiscoveryNodeRole.DATA_HOT_NODE_ROLE);
        discoBuilder.add(hotNode2);
        DiscoveryNode hotNode3 = newNode(nodeId++, DiscoveryNodeRole.DATA_HOT_NODE_ROLE);
        discoBuilder.add(hotNode3);
        DiscoveryNode warmNode1 = newNode(nodeId++, DiscoveryNodeRole.DATA_WARM_NODE_ROLE);
        discoBuilder.add(warmNode1);
        DiscoveryNode warmNode2 = newNode(nodeId++, DiscoveryNodeRole.DATA_WARM_NODE_ROLE);
        discoBuilder.add(warmNode2);
        DiscoveryNode warmNode3 = newNode(nodeId++, DiscoveryNodeRole.DATA_WARM_NODE_ROLE);
        discoBuilder.add(warmNode3);
        DiscoveryNode warmNode4 = newNode(nodeId++, DiscoveryNodeRole.DATA_WARM_NODE_ROLE);
        discoBuilder.add(warmNode4);
        DiscoveryNode warmNode5 = newNode(nodeId++, DiscoveryNodeRole.DATA_WARM_NODE_ROLE);
        discoBuilder.add(warmNode5);
        DiscoveryNode coldNode1 = newNode(nodeId, DiscoveryNodeRole.DATA_COLD_NODE_ROLE);
        discoBuilder.add(coldNode1);
        discoBuilder.localNodeId(hotNode1.getId());
        
        Metadata.Builder metadataBuilder = Metadata.builder();
        RoutingTable.Builder routingTableBuilder = RoutingTable.builder();
        IndexMetadata hotIndex1 = indexMetadata("hot_index_1", 3, 1, DataTier.DATA_HOT);
        metadataBuilder.put(hotIndex1, false).generateClusterUuidIfNeeded();
        {
            IndexRoutingTable.Builder indexRoutingTableBuilder = IndexRoutingTable.builder(hotIndex1.getIndex());