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
builder.put(dataStream);
        final ClusterState clusterState = ClusterState.builder(new ClusterName("test")).metadata(builder).build();
        ThreadPool testThreadPool = new TestThreadPool(getTestName());
        try {
            MetadataRolloverService rolloverService = DataStreamTestHelper.getMetadataRolloverService(
                dataStream,
                testThreadPool,
                Set.of(createSettingsProvider(xContentRegistry())),
                xContentRegistry()
            );
            MaxDocsCondition condition = new MaxDocsCondition(randomNonNegativeLong());
            List<Condition<?>> metConditions = Collections.singletonList(condition);
            CreateIndexRequest createIndexRequest = new CreateIndexRequest("_na_");
            MetadataRolloverService.RolloverResult rolloverResult = rolloverService.rolloverClusterState(
                clusterState,
                dataStream.getName(),
                null,
                createIndexRequest,
                metConditions,
                now,
                randomBoolean(),
                false,
                null
            );
            String sourceIndexName = DataStream.getDefaultBackingIndexName(dataStream.getName(), dataStream.getGeneration());
            String newIndexName = DataStream.getDefaultBackingIndexName(dataStream.getName(), dataStream.getGeneration() + 1);
            assertEquals(sourceIndexName, rolloverResult.sourceIndexName());
            assertEquals(newIndexName, rolloverResult.rolloverIndexName());
            Metadata rolloverMetadata = rolloverResult.clusterState().metadata();
            assertEquals(dataStream.getIndices().size() + 1, rolloverMetadata.indices().size());