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
version,
            coordinationMetadata,
            transientSettings,
            persistentSettings,
            settings,
            hashesOfConsistentSettings,
            totalNumberOfShards,
            totalOpenIndexShards,
            builder.build(),
            aliasedIndices,
            templates,
            customs,
            allIndices,
            visibleIndices,
            allOpenIndices,
            visibleOpenIndices,
            allClosedIndices,
            visibleClosedIndices,
            indicesLookup,
            mappingsByHash,
            oldestIndexVersion,
            reservedStateMetadata
        );
    }
    public Metadata withIndexSettingsUpdates(final Map<Index, Settings> updates) {
        Objects.requireNonNull(updates, "no indices to update settings for");
        final ImmutableOpenMap.Builder<String, IndexMetadata> builder = ImmutableOpenMap.builder(indices);
        updates.forEach((index, settings) -> {
            IndexMetadata previous = builder.remove(index.getName());
            assert previous != null : index;