### Elasticsearch Version

7.17, 8.x

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

Darwin

### Problem Description

The migrate to data tiers API can sometimes configure an illegal value for the `_tier_preference` setting for partially mounted indices.
This can happen if two conditions are met: 
1. if the partially mounted index doesn't have a `_tier_preference` configured
2. if the migrate to data tiers API doesn't perform any migration for this index (e.g. say this partially mounted index doesn't use the `data` custom attribute name for any allocation filtering, but either uses some other node attribute name or none at all)

In this case this piece of code kicks in to configure a default tier preference https://github.com/elastic/elasticsearch/blob/main/x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/cluster/metadata/MetadataMigrateToDataTiersRoutingService.java#L534

This is wrong, and we should configure the `MountSearchableSnapshotRequest.Storage.defaultDataTiersPreference` as the tier preference.

Relates to https://github.com/elastic/elasticsearch/issues/84758

### Steps to Reproduce

1. Mount an index - `partial-test`
2. Remove the `_tier_preference` using
```
PUT partial-test/_settings
{
  "index.routing.allocation.include._tier_preference": null
}
```
3. Call the migrate to data tiers routing API 
```
POST /_ilm/migrate_to_data_tiers
```

### Logs (if relevant)

_No response_
x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/cluster/metadata/MetadataMigrateToDataTiersRoutingService.java
String attributeValue = currentIndexSettings.get(attributeBasedRoutingSettingName);
            String convertedTierPreference = convertAttributeValueToTierPreference(attributeValue);
            if (convertedTierPreference != null) {
                newSettingsBuilder.put(TIER_PREFERENCE, convertedTierPreference);
                newSettingsBuilder.remove(attributeBasedRoutingSettingName);
                logger.debug("index [{}]: removed setting [{}]", indexName, attributeBasedRoutingSettingName);
                logger.debug("index [{}]: configured setting [{}] to [{}]", indexName, TIER_PREFERENCE, convertedTierPreference);
            } else {
                
                logger.warn(
                    "index [{}]: could not convert attribute based setting [{}] value of [{}] to a tier preference "
                        + "configuration. the only known values are: {}",
                    indexName,
                    attributeBasedRoutingSettingName,
                    attributeValue,
                    "hot,warm,cold, and frozen"
                );
                return currentIndexSettings;
            }
        }
        return newSettingsBuilder.build();
    }
    static MigratedTemplates migrateIndexAndComponentTemplates(Metadata.Builder mb, ClusterState clusterState, String nodeAttrName) {
        List<String> migratedLegacyTemplates = migrateLegacyTemplates(mb, clusterState, nodeAttrName);
        List<String> migratedComposableTemplates = migrateComposableTemplates(mb, clusterState, nodeAttrName);
        List<String> migratedComponentTemplates = migrateComponentTemplates(mb, clusterState, nodeAttrName);
        return new MigratedTemplates(migratedLegacyTemplates, migratedComposableTemplates, migratedComponentTemplates);
    }
    static List<String> migrateLegacyTemplates(Metadata.Builder mb, ClusterState clusterState, String nodeAttrName) {