### 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/test/java/org/elasticsearch/xpack/cluster/metadata/MetadataMigrateToDataTiersRoutingServiceTests.java
Map<String, Object> migratedPhaseDefAsMap = getPhaseDefinitionAsMap(newLifecycleState);
            
            
            Map<String, Object> actions = (Map<String, Object>) migratedPhaseDefAsMap.get("actions");
            assertThat(actions.size(), is(1));
            Map<String, Object> allocateDef = (Map<String, Object>) actions.get(AllocateAction.NAME);
            assertThat(allocateDef, notNullValue());
            assertThat(allocateDef.get("include"), is(Map.of()));
            assertThat(allocateDef.get("exclude"), is(Map.of()));
            assertThat(allocateDef.get("require"), is(Map.of()));
        }
        {
            
            
            LifecyclePolicyMetadata policyMetadataWithTotalShardsPerNode = getWarmColdPolicyMeta(
                warmSetPriority,
                shrinkAction,
                warmAllocateAction,
                new AllocateAction(null, 1, null, null, Map.of("data", "cold"))
            );
            LifecycleExecutionState preMigrationExecutionState = LifecycleExecutionState.builder()
                .setPhase("cold")
                .setAction("allocate")
                .setStep("allocate")
                .setPhaseDefinition(getColdPhaseDefinitionWithTotalShardsPerNode())
                .build();
            IndexMetadata.Builder indexMetadata = IndexMetadata.builder(indexName)
                .settings(getBaseIndexSettings())
                .putCustom(ILM_CUSTOM_METADATA_KEY, preMigrationExecutionState.asMap());
            ClusterState state = ClusterState.builder(ClusterName.DEFAULT)