### 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
.metadata(
                    Metadata.builder()
                        .putCustom(
                            IndexLifecycleMetadata.TYPE,
                            new IndexLifecycleMetadata(
                                Collections.singletonMap(policyMetadata.getName(), policyMetadata),
                                OperationMode.STOPPED
                            )
                        )
                        .put(indexMetadata)
                        .build()
                )
                .build();
            Metadata.Builder newMetadata = Metadata.builder(state.metadata());
            List<String> migratedPolicies = migrateIlmPolicies(newMetadata, state, "data", REGISTRY, client, null);
            assertThat(migratedPolicies.get(0), is(lifecycleName));
            ClusterState newState = ClusterState.builder(state).metadata(newMetadata).build();
            LifecycleExecutionState newLifecycleState = newState.metadata().index(indexName).getLifecycleExecutionState();
            Map<String, Object> migratedPhaseDefAsMap = getPhaseDefinitionAsMap(newLifecycleState);
            
            Map<String, Object> actions = (Map<String, Object>) migratedPhaseDefAsMap.get("actions");
            assertThat(actions.size(), is(2));
            Map<String, Object> allocateDef = (Map<String, Object>) actions.get(AllocateAction.NAME);
            assertThat(allocateDef, nullValue());
            Map<String, Object> shrinkDef = (Map<String, Object>) actions.get(ShrinkAction.NAME);
            assertThat(shrinkDef.get("number_of_shards"), is(2));
            Map<String, Object> setPriorityDef = (Map<String, Object>) actions.get(SetPriorityAction.NAME);
            assertThat(setPriorityDef.get("priority"), is(100));
            assertThat(newLifecycleState.action(), is(SetPriorityAction.NAME));
            assertThat(newLifecycleState.step(), is(SetPriorityAction.NAME));