A composable index template with no `template` defined in the body is mistakingly always assumed to not be a time series template. Even if it refers to a component template that has the `index.mode` setting set to `time_series` and the component template defines mappings with dimension fields or routing paths.

Incorrectly this causes to create a data stream with a tsdb index *without* time series start and end time settings set. The fact that this can happen is another bug and is being tracked #98833.

What should happen in this case is that a tsdb data stream is created with a valid tsdb backing index (with correctly generated time series start and end time settings).

This bug was found as part investigating #98792 and is the cause of that bug.
modules/data-streams/src/test/java/org/elasticsearch/datastreams/MetadataDataStreamRolloverServiceTests.java
import org.elasticsearch.cluster.metadata.Template;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.index.Index;
import org.elasticsearch.index.IndexMode;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.IndexVersion;
import org.elasticsearch.index.MapperTestUtils;
import org.elasticsearch.test.ESTestCase;
import org.elasticsearch.threadpool.TestThreadPool;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.xcontent.NamedXContentRegistry;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import static org.elasticsearch.cluster.metadata.IndexMetadata.SETTING_INDEX_UUID;
import static org.elasticsearch.datastreams.DataStreamIndexSettingsProvider.FORMATTER;
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.greaterThanOrEqualTo;
import static org.hamcrest.Matchers.hasItem;
import static org.hamcrest.Matchers.hasSize;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.lessThanOrEqualTo;
import static org.hamcrest.Matchers.notNullValue;
import static org.hamcrest.Matchers.nullValue;
public class MetadataDataStreamRolloverServiceTests extends ESTestCase {
    public void testRolloverClusterStateForDataStream() throws Exception {
        Instant now = Instant.now();
        String dataStreamName = "logs-my-app";