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
public void testFindAliases() {
        Metadata metadata = Metadata.builder()
            .put(
                IndexMetadata.builder("index")
                    .settings(Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, IndexVersion.current()))
                    .numberOfShards(1)
                    .numberOfReplicas(0)
                    .putAlias(AliasMetadata.builder("alias1").build())
                    .putAlias(AliasMetadata.builder("alias2").build())
            )
            .build();
        {
            GetAliasesRequest request = new GetAliasesRequest();
            Map<String, List<AliasMetadata>> aliases = metadata.findAliases(request.aliases(), Strings.EMPTY_ARRAY);