### 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 tierPreferenceConfiguration = currentIndexSettings.get(TIER_PREFERENCE);
            List<String> tiersConfiguration = DataTier.parseTierList(tierPreferenceConfiguration);
            if (tiersConfiguration.isEmpty() == false) {
                String coldestConfiguredTier = tiersConfiguration.get(0);
                String attributeValue = currentIndexSettings.get(attributeBasedRoutingSettingName);
                String attributeTierEquivalent = "data_" + attributeValue;
                if (DataTier.validTierName(attributeTierEquivalent)) {
                    
                    
                    
                    if (DataTier.compare(attributeTierEquivalent, coldestConfiguredTier) < 0) {
                        String newTierPreferenceConfiguration = convertAttributeValueToTierPreference(attributeValue);
                        if (newTierPreferenceConfiguration != null) {
                            logger.debug(
                                "index [{}]: updated the [{}] setting to [{}] as the attribute based routing setting [{}] had "
                                    + "the value [{}]",
                                indexName,
                                TIER_PREFERENCE,
                                newTierPreferenceConfiguration,
                                attributeBasedRoutingSettingName,
                                attributeValue
                            );
                            newSettingsBuilder.put(TIER_PREFERENCE, newTierPreferenceConfiguration);
                        }
                    }
                }
            }
            newSettingsBuilder.remove(attributeBasedRoutingSettingName);
            logger.debug("index [{}]: removed setting [{}]", indexName, attributeBasedRoutingSettingName);
        } else {