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.
server/src/test/java/org/elasticsearch/cluster/metadata/MetadataTests.java
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.util.set.Sets;
import org.elasticsearch.common.xcontent.XContentHelper;
import org.elasticsearch.core.Nullable;
import org.elasticsearch.core.SuppressForbidden;
import org.elasticsearch.index.Index;
import org.elasticsearch.index.IndexNotFoundException;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.IndexVersion;
import org.elasticsearch.index.alias.RandomAliasActionsGenerator;
import org.elasticsearch.index.mapper.MapperService;
import org.elasticsearch.plugins.MapperPlugin;
import org.elasticsearch.test.AbstractChunkedSerializingTestCase;
import org.elasticsearch.test.ESTestCase;
import org.elasticsearch.test.index.IndexVersionUtils;
import org.elasticsearch.xcontent.ToXContent;
import org.elasticsearch.xcontent.XContentBuilder;
import org.elasticsearch.xcontent.XContentParser;
import org.elasticsearch.xcontent.json.JsonXContent;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;