### 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
IllegalStateException illegalStateException = expectThrows(
                IllegalStateException.class,
                () -> migrateToDataTiersRouting(ilmStoppingState, "data", "catch-all", REGISTRY, client, null, false)
            );
            assertThat(illegalStateException.getMessage(), is("stop ILM before migrating to data tiers, current state is [STOPPING]"));
        }
        {
            ClusterState ilmStoppedState = ClusterState.builder(ClusterName.DEFAULT)
                .metadata(
                    Metadata.builder().putCustom(IndexLifecycleMetadata.TYPE, new IndexLifecycleMetadata(Map.of(), OperationMode.STOPPED))
                )
                .build();
            Tuple<ClusterState, MigratedEntities> migratedState = migrateToDataTiersRouting(
                ilmStoppedState,
                "data",
                "catch-all",
                REGISTRY,
                client,
                null,
                false
            );
            assertThat(migratedState.v2().migratedIndices, empty());
            assertThat(migratedState.v2().migratedPolicies, empty());
            assertThat(migratedState.v2().removedIndexTemplateName, nullValue());
        }
    }
    public void testDryRunDoesntRequireILMStopped() {
        {
            ClusterState ilmRunningState = ClusterState.builder(ClusterName.DEFAULT)
                .metadata(