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/main/java/org/elasticsearch/cluster/metadata/Metadata.java
Function<String, Predicate<String>> fieldFilter,
        Runnable onNextIndex
    ) {
        assert Transports.assertNotTransportThread("decompressing mappings is too expensive for a transport thread");
        assert concreteIndices != null;
        if (concreteIndices.length == 0) {
            return ImmutableOpenMap.of();
        }
        ImmutableOpenMap.Builder<String, MappingMetadata> indexMapBuilder = ImmutableOpenMap.builder();
        Set<String> indicesKeys = indices.keySet();
        Stream.of(concreteIndices).filter(indicesKeys::contains).forEach(index -> {
            onNextIndex.run();
            IndexMetadata indexMetadata = indices.get(index);
            Predicate<String> fieldPredicate = fieldFilter.apply(index);
            indexMapBuilder.put(index, filterFields(indexMetadata.mapping(), fieldPredicate));
        });
        return indexMapBuilder.build();
    }
    /**
     * Finds the parent data streams, if any, for the specified concrete indices.
     */
    public Map<String, DataStream> findDataStreams(String... concreteIndices) {
        assert concreteIndices != null;
        final ImmutableOpenMap.Builder<String, DataStream> builder = ImmutableOpenMap.builder();
        final SortedMap<String, IndexAbstraction> lookup = getIndicesLookup();
        for (String indexName : concreteIndices) {
            IndexAbstraction index = lookup.get(indexName);
            assert index != null;
            assert index.getType() == IndexAbstraction.Type.CONCRETE_INDEX;
            if (index.getParentDataStream() != null) {